[639a1] 1 · Every study and investigation, the humblest and the noblest alike, seems to admit of two kinds of proficiency; one of which may be properly called educated knowledge of the subject, while the other is a kind of acquaintance with it. For an [5] educated man should be able to form a fair judgement as to the goodness or badness of an exposition. To be educated is in fact to be able to do this; and the man of general education we take to be such. It will, however, of course, be understood that we only ascribe universal education to one who in his own individual person is thus [10] able to judge nearly all branches of knowledge, and not to one who has a like ability merely in some special subject. For it is possible for a man to have this competence in some one branch of knowledge.
It is plain then that, in the science which inquires into nature, there must be certain canons, by reference to which a hearer shall be able to criticize the method of a professed exposition, quite independently of the question whether the [15] statements made be true or false. Ought we, for instance (to give an illustration of what I mean), to begin by discussing each separate substance—man, lion, ox, and the like—taking each kind in hand independently of the rest, or ought we rather to lay down the attributes which they have in common in virtue of some common [20] element of their nature? For genera that are quite distinct present many identical phenomena, sleep, for instance, respiration, growth, decay, death, and other similar affections and conditions that may remain; for at present it is an obscure and indeterminate business to discuss them. Now it is plain that if we deal with each species independently of the rest, we shall frequently be obliged to repeat the same [25] statements over and over again; for horse and dog and man present every one of the phenomena just enumerated. A discussion therefore of the attributes of each such species separately would necessarily involve frequent repetitions as to characters, themselves identical but recurring in animals specifically distinct. (Very possibly also there may be other characters which, though they present specific differences, yet come under one and the same category. For instance, flying, swimming, [639b1] walking, creeping, are plainly specifically distinct, but yet are all forms of animal progression.) We must, then, have some clear understanding as to the manner in which our investigation is to be conducted; whether, I mean, we are first to deal with the common or generic characters, and afterwards to take into consideration special [5] peculiarities; or whether we are to start straight off with the particular species. For as yet no definite rule has been laid down in this matter. So also there is a like uncertainty as to another point now to be mentioned. Ought the student of nature follow the plan adopted by the mathematicians in their astronomical demonstrations, and after considering the phenomena presented by animals, and their several parts, proceed subsequently to treat of the causes and the reason why; or ought he to [10] follow some other method? Furthermore, the causes concerned in natural generation are, as we see, more than one. There is the cause for the sake of which, and the cause whence the beginning of motion comes. Now we must decide which of these two causes comes first, which second. Plainly, however, that cause is the first which we call that for the sake of which. For this is the account of the thing, and the [15] account forms the starting-point, alike in the works of art and in works of nature. For the doctor and the builder define health or house, either by the intellect or by perception, and then proceed to give the accounts and the causes of each of the things they do and of why they should do it thus. Now in the works of nature the good and that for the sake of which is still more dominant than in works of art, nor is [20] necessity a factor with the same significance in them all; though almost all writers try to refer their accounts to this, failing to distinguish the several ways in which necessity is spoken of. For there is absolute necessity, manifested in eternal phenomena; and there is hypothetical necessity, manifested in everything that is [25] generated as in everything that is produced by art, be it a house or what it may. For if a house or other such final object is to be realized, it is necessary that first this and then that shall be produced and set in motion, and so on in continuous succession, [30] until the end is reached, for the sake of which each prior thing is produced and exists. So also is it with the productions of nature. The mode of necessity, however, [640a1] and the mode of demonstration are different in natural science from what they are in the theoretical sciences (we have spoken of this elsewhere). For in the latter the starting-point is that which is; in the former that which is to be. For since health, or a man, is of such and such a character, it is necessary for this or that to exist or be [5] produced; it is not the case that, since this or that exists or has been produced, that of necessity exists or will exist. Nor is it possible to trace back the necessity of demonstrations of this sort to a starting-point, of which you can say that, since this exists, that exists. These however, again, are matters that have been dealt with in another treatise, where it was stated where necessity is present, where it is [10] reciprocal and for what reason.1
Another matter which must not be passed over without consideration is, whether the proper subject of our exposition is that with which the earlier writers concerned themselves, namely, the way each thing is naturally generated, or rather the way it is. For there is no small difference between these two views. The best course appears to be that we should follow the method already mentioned—begin [15] with the phenomena presented by each group of animals, and, when this is done, proceed afterwards to state the causes of those phenomena—in the case of generation too. For in house building too, these things come about because the form of the house is such and such, rather than its being the case that the house is such and such because it comes about thus. For the generation is for the sake of the substance and not this for the sake of the generation. Empedocles, then, was in error [20] when he said that many of the characters presented by animals were merely the results of incidental occurrences during their development; for instance, that the backbone is as it is because it happened to be broken owing to the turning of the foetus in the womb. In so saying he overlooked the fact that propagation implies a creative seed endowed with certain powers. Secondly, he neglected another fact, namely, that the parent animal pre-exists, not only in account, but actually in time. [25] For man is generated from man; and thus it is because the parent is such and such that the generation of the child is thus and so. [The same statement holds good also for those which are apparently spontaneous, as also for the products of art. For the [30] same result as is produced by art may occur spontaneously, e.g. health. Those things whose agent is pre-existent, such as the statuary’s art, cannot possibly be produced spontaneously. Art indeed consists in the account of the product without its matter. So too with chance products; for they are produced in the same way as products of art.]2
The fittest mode, then, of treatment is to say, a man has such and such parts, because the essence of man is such and such, and because they are necessary [35] conditions of his existence, or, if we cannot quite say this then the next thing to it, namely, that it is either quite impossible for a man to exist without them, or, at any [640b1] rate, that it is good that they should be there. And this follows: because man is such and such the process of his development is necessarily such as it is; and therefore this part is formed first, that next; and after a like fashion should we explain the generation of all other works of nature.
[5] Now that with which the ancient writers, who first philosophized about nature, busied themselves, was the material principle and the material cause. They inquired what this is, and what its character; how the universe is generated out of it, and by what motor influence, whether, for instance, by strife or love or mind or spontaneous action, the substratum of matter being assumed to have of necessity a certain nature—fire, for instance, to have a hot nature, earth a cold one; the former [10] to be light, the latter heavy. For even the genesis of the universe is thus explained by them. After a like fashion do they deal also with the development of plants and of animals. They say, for instance, that the water contained in the body causes by its currents the formation of the stomach and the other receptacles of food or of [15] excretion; and that the breath by its passage breaks open the outlets of the nostrils; air and water being the materials of which bodies are made; for all represent nature as composed of such or similar substances.
But if men and animals and their several parts are natural phenomena, then the natural philosopher must take into consideration flesh, bone, blood, and all the other homogeneous parts; not only these, but also the heterogeneous parts, such as [20] face, hand, foot; and must examine how each of these comes to be what it is, and in virtue of what force. For it is not enough to say what are the stuffs out of which an animal is formed, to state, for instance, that it is made of fire or earth—if we were discussing a couch or the like, we should try to determine its form rather than its matter (e.g. bronze or wood), or if not, we should give the matter of the whole. For a [25] couch is such and such a form embodied in this or that matter, or such and such a matter with this or that form; so that its shape and structure must be included in our description. For the formal nature is of greater importance than the material nature.
Does, then, configuration and colour constitute the essence of the various [30] animals and of their several parts? For if so, what Democritus says will be correct. For such appears to have been his notion. At any rate he says that it is evident to every one what form it is that makes the man, seeing that he is recognizable by his shape and colour. And yet a dead body has exactly the same configuration as a [35] living one; but for all that is not a man. So also no hand of bronze or wood or constituted in any but the appropriate way can possibly be a hand in more than [641a1] name. For like a physician in a painting, or like a flute in a sculpture, it will be unable to perform its function. Precisely in the same way no part of a dead body, such I mean as its eye or its hand, is really an eye or a hand. What he says, then, is [5] too simple—it is much the same as if a woodcarver were to insist that the hand he had cut out was really a hand. Yet the physiologists, when they give an account of the development and causes of the animal form, speak very much like such a craftsman. What are the forces by which the hand or the body was fashioned into its shape? The woodcarver will perhaps say, by the axe or the auger; the physiologist, by air and by earth. Of these two answers the woodcarver’s is the better. For it is not [10] enough for him to say that by the stroke of his tool this part was formed into a concavity, that into a flat surface; but he must state the reasons why he struck his blow in such a way as to effect this, and for the sake of what he did so; namely, that the piece of wood should develop eventually into this or that shape. It is plain, then, that they are wrong, and that the true method is to state what the characters are [15] that distinguish the animal—to explain what it is and what are its qualities—and to deal after the same fashion with its several parts; in fact, to proceed in exactly the same way as we should do, were we dealing with the form of a couch.
If now the form of the living being is the soul, or part of the soul, or something that without the soul cannot exist; as would seem to be the case, seeing at any rate that when the soul departs, what is left is no longer an animal, and that none of the parts remain what they were before, excepting in mere configuration, like the [20] animals that in the fable are turned into stone; if, I say, this is so, then it will come within the province of the natural scientist to inform himself concerning the soul, and to treat of it, either in its entirety, or, at any rate, of that part of it which constitutes the essential character of an animal; and it will be his duty to say what a soul or this part of a soul is; and to discuss the attributes that attach to this essential character, especially as nature is spoken of—and is—twofold, as matter and as [25] substance; nature as substance including both the motor cause and the final cause. Now it is in the latter of these two senses that either the whole soul or some part of it constitutes the nature of an animal; and inasmuch as it is the presence of the soul that enables matter to constitute the animal nature, much more than it is the [30] presence of matter which so enables the soul, the inquirer into nature is bound to treat of the soul rather than of the matter. For though the wood of which they are made constitutes the couch and the tripod, it only does so because it is potentially such and such a form.
What has been said suggests the question, whether it is the whole soul or only some part of it, the consideration of which comes within the province of natural [35] science. Now if it be of the whole soul that this should treat, then there is no place for any other philosophy beside it. For as it belongs in all cases to one and the same science to deal with correlated subjects—one and the same science, for instance, deals with sensation and with the objects of sense—and as therefore the intelligent [645b1] soul and the objects of intellect, being correlated, must belong to one and the same science, it follows that natural science will have to include everything in its province. [5] But perhaps it is not the whole soul, nor all its parts collectively, that constitutes the source of motion; but there may be one part, identical with that in plants, which is the source of growth, another, namely the sensory part, which is the source of change of quality, while still another, and this not the intellectual part, is the source of locomotion. For other animals than man have the power of locomotion, but in none but him is there intellect. Thus then it is plain that it is not of the whole soul that we have to treat. For it is not the whole soul that constitutes the animal nature, [10] but only some part or parts of it. Moreover, it is impossible that any abstraction can form a subject of natural science, seeing that everything that nature makes is for the sake of something. For just as art is present in the products of art, so in the things [15] themselves there is evidently an analogous cause or principle derived like the hot and the cold from the environing universe. And that the heaven, if it had an origin, was generated and is maintained by such a cause, there is therefore even more reason to believe, than that mortal animals so originated. For order and definiteness are much more plainly manifest in the celestial bodies than in our own frame; while [20] change and chance are rather characteristic of the perishable things of earth. Yet there are some who, while they allow that every animal exists and was generated by nature, nevertheless hold that the heaven was constructed to be what it is by chance and spontaneity; the heaven, in which not the faintest sign of chance or of disorder is discernible. Again, whenever there is plainly some final end, to which a motion [25] tends should nothing stand in the way, we always say that the one is for the sake of the other; and from this it is evident that there must be something of the kind, corresponding to what we call nature. For a given seed does not give rise to any chance living being, nor spring from any chance one; but each springs from a definite parent. And thus it is that from which the seed comes which is the origin and fabricator of its offspring. For these it is by nature, the offspring being at any [30] rate that which in nature will spring from it. At the same time the offspring is prior to the seed; for the seed is a coming into being, the end a substance. Prior, however, to both is the organism from which the seed was derived. For we speak of seeds in two ways, mentioning that from which it comes and that to which it gives rise: it is both the seed of that from which it came, of the horse, for instance, and the seed of the organism that will eventually arise from it, of the mule, for example—the seed [35] of both, though in different ways as here set forth. Moreover, the seed is potentially something, and the relation of potentiality to actuality we know.
There are then two causes, namely, necessity and the final end. For many [642a1] things are produced, simply as the results of necessity. It may, however, be asked, of what mode of necessity are we speaking when we say this. For it can be of neither of [5] those two modes which are set forth in the philosophical treatises. There is, however, the third mode, in such things at any rate as are generated. For instance, we say that food is necessary in neither of the two modes, but because an animal cannot possibly do without it. This third mode is what may be called hypothetical necessity. For if a piece of wood is to be split with an axe, the axe must of necessity [10] be hard; and, if hard, must of necessity be made of bronze or iron. Now exactly in the same way the body, since it is an instrument—for both the body as a whole and its several parts individually are for the sake of something—if it is to do its work, must of necessity be of such and such a character, and made of such and such materials.
It is plain then that there are two modes of causation, and that both of these must, so far as possible, be taken into account, or that at any rate an attempt must [15] be made to include them both; and that those who fail in this tell us in reality nothing about nature. For nature of an animal is a first principle rather than matter. There are indeed passages in which even Empedocles hits upon this, and following the guidance of fact, finds himself constrained to speak of the ratio as constituting [20] the substance and nature of things. Such, for instance, is the case when he explains what is a bone. For he does not say it is this one element, or those two or three elements, or a compound of all the elements, but states the ratio of their combination. As with a bone, so manifestly is it with the flesh and all other similar parts.
The reason why our predecessors failed to hit on this method of treatment was, [25] that they were not in possession of the notion of essence, nor of any definition of substance. The first who came near it was Democritus, and he was far from adopting it as a necessary method in natural science, but was merely brought to it by constraint of facts. In the time of Socrates a nearer approach was made to the method. But at this period men gave up inquiring into nature, and philosophers diverted their attention to political science and to the virtues which benefit [30] mankind.
Of the method itself the following is an example. In dealing with respiration we must show that it takes place for such or such a final object; and we must also show that this and that part of the process is necessitated by this and that other stage of it. By necessity we shall sometimes mean that the requisite antecedents must be there, if the final end is to be reached; and sometimes that things are thus and so by nature. For the alternate discharge and re-entrance of heat and the inflow of air are necessary—that is necessary; and as the internal heat resists in the process of [642b1] cooling, the entrance and exit of the external air occur.
In the foregoing we have an example of the method which we must adopt, and also an example of the kind of phenomena, the causes of which we have to investigate.
[5] 2 · Some writers propose to reach the ultimate forms of animal life by dividing the genus into two differences. But this method is often difficult, and often impracticable.
Sometimes one differentia is sufficient by itself, and the others are mere surplusage. Thus in the series Footed, Two-footed, Cleft-footed, the last term alone is significant, and to append the others is only an idle iteration.
[10] Again it is not permissible to break up a natural group, Birds for instance, by putting its members under different bifurcations, as is done in the published dichotomies, where some birds are ranked with animals of the water, and others placed in a different class. The group Birds and the group Fishes happen to be named, while other natural groups have no names; for instance, the groups that we [15] may call Sanguineous and Bloodless are not known popularly by any one name. If such natural groups are not to be broken up, the method of dichotomy cannot be employed, for it necessarily involves such breaking up and dislocation. The group of [20] the Many-footed, for instance, would have some of its kinds distributed among land animals, others among water animals.
3 · Again, privative terms inevitably form one branch of dichotomous division, as we see in the proposed dichotomies. But privative terms in their character of privatives admit of no subdivision. For there can be no specific forms of a negation, of Featherless for instance or of Footless, as there are of Feathered and [25] of Footed. Yet a generic differentia must be subdivisible; for otherwise what is there that makes it generic rather than specific? There are to be found generic, that is specifically subdivisible, differentiae; Feathered for instance and Footed. For feathers are divisible into Barbed and Unbarbed, and feet into Manycleft, and Twocleft, like those of animals with bifid hoofs, and Uncleft or Undivided, like [30] those of animals with solid hoofs. Now even with differentiae capable of this specific subdivision it is difficult enough so to make the classification that each animal shall be comprehended in some one subdivision and in not more than one (e.g. winged and wingless; for some are both—e.g. ants, glowworms, and some others); but far more [35] difficult, impossible, is it to do this, if we start with a dichotomy into two contradictories. For each differentia must be presented by some species. There must [643a1] be some species, therefore, under the privative heading. Now specifically distinct animals cannot present in their substance a common undifferentiated element, but any apparently common element must really be differentiated. (Bird and Man for instance are both Two-footed, but their two-footedness is diverse and differentiated. And if they are sanguineous they must have some difference in their blood, if their [5] blood is part of their substance.) From this it follows that one differentia will belong to two species; and if that is so, it is plain that a privative cannot be a differentia.
Again, if the species are indivisible and the differentiae are indivisible, and if no differentia be common to several groups, the number of differentiae must be equal to the number of species. If a differentia though not divisible could yet be common to several groups, then it is plain that in virtue of that common differentia [10] specifically distinct animals would fall into the same division. It is necessary then, if the differentiae, under which are ranged all the indivisible groups, are specific characters, that none of them shall be common; for otherwise, as already said, specifically distinct animals will come into one and the same division. But no one indivisible group must be included in more than a single division; different groups must not be included in the same division; and every group must be found in some [15] division. It is plain then that we cannot get at the indivisible species of the animal, or any other, kingdom by bifurcate division. If we could, the number of ultimate differentiae would equal the number of indivisible animal species. For assume an [20] order of beings whose prime differentiae are White and Non-white. Each of these branches will bifurcate, and their branches again, and so on till we reach the differentiae, whose number will be four or some other power of two, and will also be the number of the ultimate species.
(A species is constituted by the combination of differentia and matter. For no part of an animal is purely material or purely immaterial; nor can a body, [25] independently of its condition, constitute an animal or any of its parts, as has repeatedly been observed.)
Further, the differentiae must be elements of the substance, and not merely essential attributes. Thus if Figure is the term to be divided, it must not be divided into figures whose angles are equal to two right angles, and figures whose angles are together greater than two right angles. For it is only an attribute of a triangle that [30] its angles are equal to two right angles.
Again, the bifurcations must be opposites, for opposites are different from one another—e.g. White and Black, Straight and Bent; and if we characterize one branch by either term, we must characterize the other by its opposite, and not, for example, characterize one branch by a colour, the other by an inclination. [35]
Furthermore, living beings cannot be divided by the functions common to body and soul, by Flying, for instance, and Walking, as we see them divided in the dichotomies already referred to. For some groups, Ants for instance, fall under both [643b1] divisions, some ants flying while others do not. Similarly as regards the division into Wild and Tame; for it also would involve the disruption of a species into different groups. For in almost all species in which some members are tame, there are other [5] members that are wild. Such, for example, is the case with Men, Horses, Oxen, Dogs in India, Pigs, Goats, Sheep: groups which if they have the same name, have not been divided, and which, if single, prove that Wildness and Tameness do not amount to specific differences. And whatever differentia we take as a basis of division the same difficulty will occur.
We must attempt to recognize the natural groups, following the indications [10] afforded by the instincts of mankind, which led them for instance to form the class of Birds and the class of Fishes, each of which groups combines a multitude of differentiae, and is not defined by a single one as in dichotomy. The method of dichotomy is either impossible (for it would put a single group under different [15] divisions or contrary groups under the same division), or it only furnishes a single differentia for each species, which either alone or in combination has to constitute the ultimate species.
If, again, they do not take a differentia of the differentia, they are bound to make their division continuous only in the sense in which a sentence is one by conjunction. For instance, suppose we have the bifurcation Feathered and Featherless, [20] and then divide Feathered into Wild and Tame, or into White and Black. Tame and White are not a differentiation of Feathered, but are the commencement of an independent bifurcation, and are here by accident.
As we said then, we must define at the outset by a multiplicity of differentiae. [25] If we do so, privative terms will be available, which are unavailable to the dichotomist.
The impossibility of reaching the definition of any of the ultimate forms by dichotomy of the larger group, as some propose, is manifest also from the following considerations. It is impossible that a single differentia, either by itself or in [30] combination shall express the whole of a species. [In saying a single differentia by itself I mean one which has no differentia as Cleft-footed; in saying a single differentia in combination I mean, to give an instance, Many-cleft-footed as related to Cleft-footed.]3 The very continuity of a series of successive differentiae in a [35] division is intended to show that the whole is a unity. But one is misled by the usages of language into imagining that it is merely the final term of the series [Many-cleft-footed or Two-footed for instance]4 that constitutes the whole differentia, [and [644a1] that Footed Cleft-footed, are superfluous]5 Now it is evident that such a series cannot consist of many terms. For if one divides and subdivides, one soon reaches the final differential term, [but for all that will not have got to the ultimate division, [5] that is, to the species.]6 Suppose, for example, Man to be the animal to be defined; the single differentia will be Cleft-footed, either by itself or with its antecedents, Footed and Two-footed. Now if man was nothing more than a Cleft-footed animal, this single differentia would duly represent his essence. But seeing that this is not the case, more differentiae than this one will necessarily be required to define him; and these cannot come under one division; for each single branch of a dichotomy [10] ends in a single differentia, and cannot possibly include several differentiae belonging to one and the same animal.
It is impossible then to reach any of the ultimate animal forms by dichotomous division.
4 · It deserves inquiry why a single name denoting a higher group was not invented by mankind, as an appellation to comprehend the two groups of Water [15] animals and Winged animals. For even these have certain attributes in common. However, the present nomenclature is just. Groups that only differ in degree, and in the more or less of an identical element that they possess, are aggregated under a single class; groups whose attributes are only analogous are separated. For instance, bird differs from bird by gradation, or by excess and defect—some birds have long [20] feathers, others short ones. Bird and Fish only agree in having analogous organs; for what in the bird is feather, in the fish is scale. It is not easy to do this in all cases; for in most animals what is common is so by analogy.
Since the ultimate species are substances and individuals which do not differ in species are found in them (e.g. Socrates, Coriscus), we must either describe the [25] universal attributes first or else say the same thing many time over, as I said. (The universal attributes are common; for we call universal those which belong to more than one subject.)
One may wonder which of two courses to follow. For on the one hand it may be urged that as the ultimate species represent substances, it will be well, if practicable, to examine these ultimate species separately, as Man, and Bird—for [30] this genus contains species: about every indivisible species, then, e.g. Sparrow, Crane, and the like.
On the other hand, however, this course would involve repeated mention of the same attribute, as the same attribute is common to many species, and so far would be somewhat irrational and tedious. Perhaps, then, it will be best to treat generically [644b1] the universal attributes of the groups that have a common nature and contain closely allied subordinate forms, whether they are groups recognized by popular usage, such as Birds and Fishes, or groups not popularly known by a common [5] appellation, but composed of closely allied subordinate groups; and only to deal individually with the attributes of a single species, when such species—man, for instance, and any other such, if such there be—are not of that sort.
It is generally similarity in the shape of particular organs, or of the whole body, that has determined the formation of the larger groups. It is in virtue of such a similarity that Birds, Fishes, Cephalopoda, and Testacea have been made to form [10] each a separate class. For within the limits of each such class, the parts do not differ in that they have no nearer resemblance than that of analogy—such as exists between the bone of man and the spine of fish—but differ merely in respect of such corporeal conditions as largeness smallness, softness hardness, smoothness roughness, and other similar oppositions, or, in one word, in respect of degree. [15]
We have now touched upon the canons for criticizing the method of natural science, and have considered what is the most systematic and easy course of investigation; we have also dealt with division, and the mode of conducting it so as best to attain the ends of science, and have shown why dichotomy is either impracticable or inefficacious for its professed purposes.
Having laid this foundation, let us pass on to our next topic. [20]
5 · Of substances constituted by nature some are ungenerated, imperishable, and eternal, while others are subject to generation and decay. The former are excellent and divine, but less accessible to knowledge. The evidence that might [25] throw light on them, and on the problems which we long to solve respecting them, is furnished but scantily by sensation; whereas respecting perishable plants and animals we have abundant information, living as we do in their midst, and ample [30] data may be collected concerning all their various kinds, if only we are willing to take sufficient pains. Both departments, however, have their special charm. The scanty conceptions to which we can attain of celestial things give us, from their excellence, more pleasure than all our knowledge of the world in which we live; just as a half glimpse of persons that we love is more delightful than an accurate view of [645a1] other things, whatever their number and dimensions. On the other hand, in certitude and in completeness our knowledge of terrestrial things has the advantage. Moreover, their greater nearness and affinity to us balances somewhat the loftier interest of the heavenly things that are the objects of the higher philosophy. Having [5] already treated of the celestial world, as far as our conjectures could reach, we proceed to treat of animals, without omitting, to the best of our ability, any member of the kingdom, however ignoble. For if some have no graces to charm the sense, yet nature, which fashioned them, gives amazing pleasure in their study to all who can [10] trace links of causation, and are inclined to philosophy. Indeed, it would be strange if mimic representations of them were attractive, because they disclose the mimetic skill of the painter or sculptor, and the original realities themselves were not more [15] interesting, to all at any rate who have eyes to discern the causes. We therefore must not recoil with childish aversion from the examination of the humbler animals. Every realm of nature is marvellous: and as Heraclitus, when the strangers who came to visit him found him warming himself at the furnace in the kitchen and [20] hesitated to go in, is reported to have bidden them not to be afraid to enter, as even in that kitchen divinities were present, so we should venture on the study of every kind of animal without distaste; for each and all will reveal to us something natural and something beautiful. Absence of haphazard and conduciveness of everything to an end are to be found in nature’s works in the highest degree, and the end for which [25] those works are put together and produced is a form of the beautiful.
If any person thinks the examination of the rest of the animal kingdom an unworthy task, he must hold in like disesteem the study of man. For no one can look at the elements of the human frame—blood, flesh, bones, vessels, and the [30] like—without much repugnance. Moreover, when any one of the parts or structures, be it which it may, is under discussion, it must not be supposed that it is its material composition to which attention is being directed or which is the object of the discussion, but rather the total form. Similarly, the true object of architecture is not bricks, mortar, or timber, but the house; and so the principal object of natural philosophy is not the material elements, but their composition, and the totality of [645b1] the substance, independently of which they have no existence.
The course of exposition must be first to state the essential attributes common to whole groups of animals, and then to attempt to give their explanation. Many groups, as already noticed, present common attributes, that is to say, in some cases [5] absolutely identical—feet, feathers, scales, and the like; while in other groups the affections and organs are analogous. For instance, some groups have lungs, others have no lung, but an organ analogous to a lung in its place; some have blood, others [10] have no blood, but a fluid analogous to blood, and with the same office. To treat of the common attributes separately in connexion with each individual group would involve, as already suggested, useless iteration. For many groups have common attributes. So much for this topic.
As every instrument and every bodily member is for the sake of something, viz. [15] some action, so the whole body must evidently be for the sake of some complex action. Thus the saw is made for sawing, for sawing is a function, and not sawing for the saw. Similarly, the body too must somehow or other be made for the soul, and each part of it for some subordinate function, to which it is adapted. [20]
We have, then, first to describe the common functions, and those which belong to a genus or to a species. By ‘common’ I mean those which belong to all animals; by to a genus’, those of animals whose differences from one another we see to be matters of degree—Bird is a genus. Man is a species, and so is everything not [25] differentiated into subordinate groups. In the first case the common attributes may be called analogous, in the second generic, in the third specific.
When a function is ancillary to another, a like relation manifestly obtains between the organs which discharge these functions; and similarly, if one function is prior to and the end of another, their respective organs will stand to each other in [30] the same relation. Thirdly, there are functions which are the necessary consequences of others.
Instances of what I mean by functions and affections are Reproduction, Growth, Copulation, Waking, Sleep, Locomotion, and other similar animal actions. Instances of what I mean by parts are Nose, Eye, Face, and other so-called [646a1] members; and similarly for the rest. So much for the method to be pursued. Let us now try to set forth the causes of all these things, both common and special, and in so doing let us follow that order of exposition which conforms, as we have indicated, to the order of nature.
1 · The nature and the number of the parts of which animals are severally composed are matters which have already been set forth in detail in the book of Histories about animals. We have now to inquire what are the causes that in each [10] case have determined this composition, a subject quite distinct from that dealt with in the Histories.
Now there are three degrees of composition; and of these the first in order, as all will allow, is composition out of what some call the elements, such as earth, air, water, fire. Perhaps, however, it would be more accurate to say composition out of [15] the elementary forces; nor indeed out of all of these, as said elsewhere in previous treatises. For wet and dry, hot and cold, form the material of all composite bodies; and all other differences are secondary to these, such differences, that is, as heaviness or lightness, density or rarity, roughness or smoothness, and any other [20] such properties of bodies as there may be. The second degree of composition is that by which the homogeneous parts of animals, such as bone, flesh, and the like, are constituted out of the primary substances. The third and last stage is the composition which forms the heterogeneous parts, such as face, hand, and the rest.
[25] Now the order of development and the order of substance are always the inverse of each other. For that which is posterior in the order of development is antecedent in the order of nature, and that is genetically last which in nature is first.
(That this is so is manifest by induction; for a house does not exist for the sake of bricks and stones, but these materials for the sake of the house; and the same is [30] the case with the materials of other bodies. And the same thing can be shown by argument. For generation is a process from something to something, from a principle to a principle—from the primary efficient cause, which is something already endowed with a certain nature, to some definite form or similar end; for [35] man generates man, and plant generates plant, in each case out of the underlying material.)
[646b1] In order of time, then, the material and the generative process must necessarily be anterior; but in logical order the substance and form of each being precedes the material. This is evident if one only tries to define the process of formation. For the definition of house-building includes that of the house; but the definition of the [5] house does not include that of house-building; and the same is true of all other productions. So that it must necessarily be that the elementary material exists for the sake of the homogeneous parts, seeing that these are genetically posterior to it, just as the heterogeneous parts are posterior genetically to them. For these heterogeneous parts have reached the end and goal, having the third degree of [10] composition, in which development often attains its final term.
Animals, then, are composed of homogeneous parts, and are also composed of heterogeneous parts. The former, however, exist for the sake of the latter. For the active functions and operations of the body are carried on by these; that is, by the heterogeneous parts, such as the eye, the nostril, the whole face, the fingers, the [15] hand, and the whole arm. But inasmuch as there is a great variety in the functions and motions not only of the whole animal but also of the individual organs, it is necessary that the substances out of which these are composed shall present a diversity of powers. For some purposes softness is advantageous, for others hardness; some parts must be capable of extension, others of flexion. Such powers, [20] then, are distributed separately to the different homogeneous parts, one being soft another hard, one wet another dry, one viscous another brittle; whereas each of the heterogeneous parts presents a combination of multifarious powers. For the hand, to take an example, requires one power to enable it to effect pressure, and another [25] for simple prehension. For this reason the instrumental parts of the body are compounded out of bones, sinews, flesh, and the like, but not these latter out of the former.
So far, then, as has yet been stated, the relations between these two orders of parts are determined by a final cause. We have, however, to inquire whether necessity may not also have a share in the matter; and it must be admitted that these [30] mutual relations could not from the very beginning have possibly been other than they are. For heterogeneous parts can be made up out of homogeneous parts, either from a plurality of them, or from a single one, as is the case with some of the viscera which, varying in configuration, are yet, to speak broadly, formed from a single homogeneous substance; but that homogeneous substances should be formed out of a combination of heterogeneous parts is clearly an impossibility—for then a homogeneous thing would consist of many heterogeneous things. For these causes, then, some parts of animals are simple and homogeneous, while others are [647a1] composite and heterogeneous; and dividing the parts into the instrumental and the sensitive, each one of the former is, as before said, heterogeneous, and each one of [5] the latter homogeneous. For each sense is confined to a single order of sensibles, and its organ must be such as to admit that order. But that which is endowed with a property potentially acted on by that which has the like property actually, so that the two are the same in kind, and if the latter is single so also is the former. Thus it is [10] that while no physiologists ever dream of saying of the hand or face or other such part that one is earth, another water, another fire, they couple each separate sense-organ with a separate element, asserting this one to be air and that other to be fire.
Sensation, then, is confined to the simple or homogeneous parts. But, as might reasonably be expected, the organ of touch, though still homogeneous, is yet the [15] least simple of all the sense-organs. For touch more than any other sense appears to be correlated to several distinct kinds of objects, and to recognize more than one category of contrasts, heat and cold, for instance, dry and wet, and other similar oppositions. Accordingly, the organ which deals with these varied objects is of all the sense-organs the most corporeal, being either the flesh, or the substance which [20] in some animals takes the place of flesh.
Now as there cannot possibly be an animal without sensation, it follows as a necessary consequence that every animal must have some homogeneous parts; for these alone are capable of sensation, the heterogeneous parts serving for the active functions. Again, as the sensory faculty, the motor faculty, and the nutritive faculty [25] are all lodged in one and the same part of the body, as was stated in a former treatise, it is necessary that the part which is the primary seat of these principles shall on the one hand, in its character of general sensory recipient, be one of the simple parts; and on the other hand shall, in its motor and active character, be one of the heterogeneous parts. For this reason it is the heart which in sanguineous animals [30] constitutes this central part, and in bloodless animals it is that which takes the place of a heart. For the heart, like the other viscera, divides into homogeneous parts; but it is at the same time heterogeneous in virtue of its definite configuration. And the same is true of the other so-called viscera, which are indeed formed from the same material as the heart. For all these viscera have a sanguineous character owing to [647b1] their being situated upon vascular ducts and branches. For just as a stream of water deposits mud, so the various viscera, the heart excepted, are, as it were, deposits from the stream of blood in the vessels. And as to the heart, the very starting-point of the vessels, and the actual seat of the force by which the blood is first fabricated, [5] it is as one would naturally expect, constituted out of the selfsame nutriment which it originates. Such, then, are the reasons why the viscera are of sanguineous aspect; and why in one point of view they are homogeneous, in another heterogeneous.
[10] 2 · Of the homogeneous parts of animals, some are soft and moist, others hard and dry; and of the former some are moist permanently, others only so long as they are in the living body. Such are blood, serum, lard, suet, marrow, semen, bile, milk when present, flesh, and their various analogues. For the parts enumerated are [15] not to be found in all animals, some animals only having parts analogous to them. Of the hard and dry homogeneous parts bone, fish-spine, sinew, blood-vessel, are examples. The last of these points to a sub-division that may be made in the class of homogeneous parts. For in some of them the whole and a portion of the whole in one sense are designated by the same term—as, for example, is the case with blood-vessel and bit of blood-vessel—while in another sense they are not; but a [20] portion of a heterogeneous part, such as face, in no sense has the same designation as the whole.
First, both the moist parts and the dry parts have causes of many kinds. Thus one set of homogeneous parts represent the material; for each separate organ is [25] constructed of bones, sinews, flesh, and the like; which contribute either to its substance or to the proper discharge of its function. A second set are the nutriment of the first, and are moist; for all growth comes from moisture; while a third set are the residue of the second. Such, for instance, are the dregs of the solid nutriment, and—in animals that have a bladder—those of the liquid.
Even the individual homogeneous parts present variations, which are in each [30] case for the sake of the better. The variations of the blood may be selected to illustrate this. For different bloods differ in their degrees of thinness or thickness, of clearness or turbidity, of coldness or heat; and this whether we compare the bloods from different parts of the same individual or the bloods of different animals. For all the differences just enumerated distinguish the blood of the upper and of the lower [648a1] halves of the body; and one section of animals is sanguineous, while the other has no blood, but only something resembling it in its place. The thicker and the hotter blood is, the more conducive is it to strength, while in proportion to its thinness and its coldness is its suitability for sensation and intelligence. A like distinction exists [5] also in the fluid which is analogous to blood. This explains how it is that bees and other similar creatures are of a more intelligent nature than many sanguineous animals; and that, of sanguineous animals, those are the most intelligent whose blood is thin and cold. Best of all are those whose blood is hot, and at the same time [10] thin and clear. For such are suited alike for the development of courage and of intelligence. Accordingly, the upper parts are superior in these respects to the lower, the male superior to the female, and the right side to the left. As with the blood so [15] also with the other parts, homogeneous and heterogeneous alike. For here also such variations as occur must be held either to be related to the substance and the functions of the several animals, or, in other cases, to be matters of better or worse. Two animals, for instance, may have eyes. But in one these eyes may be of fluid consistency, while in the other they are hard; and in one there may be eyelids, in the other no such appendages. In both cases the difference contributes to greater accuracy of vision.
As to why all animals must of necessity have blood or something of a similar [20] character, and what the nature of blood may be, these are matters which can only be considered when we have first discussed hot and cold. For the natural properties of many substances are referable to these two elementary principles; and it is a matter of frequent dispute what animals or what parts of animals are hot and what cold. [25] For some maintain that water animals are hotter than such as live on land, asserting that their natural heat counterbalances the coldness of their medium; and again, that bloodless animals are hotter than those with blood, and females than males. Parmenides, for instance, and some others declare that women are hotter than men, and that it is the warmth and abundance of their blood which causes their [30] menstrual flow, while Empedocles maintains the opposite opinion. Again, comparing the blood and the bile, some speak of the former as hot and of the latter as cold, while others invert the description. If there be this endless disputing about hot and cold, which of all things that affect our senses are the most distinct, what are we to [35] think as to the rest?
The explanation of the difficulty appears to be that things are called hotter in several ways; for each appears to have something to say, although they are at odds [648b1] with one another. There ought, then, to be some clear understanding as to the sense in which natural substances are to be termed hot or cold, dry or moist. For it appears manifest that these are properties on which even life and death are largely dependent, and that they are moreover the causes of sleep and waking, of maturity [5] and old age, of health and disease; while no similar influence belongs to roughness and smoothness, to heaviness and lightness, nor, in short, to any other such properties of matter. That this should be so is but in accordance with rational expectation. For hot and cold, dry and moist, as was stated in a former treatise, are [10] the principles of the natural elements.
Is then the term hot used in one way or in many? To answer this we must ascertain what special effect is attributed to a hotter substance, and if there be several such, how many these may be. A body then is in one sense said to be hotter than another, if it imparts a greater amount of heat to an object in contact with it. In a second sense, that is said to be hotter which causes the keener sensation when [15] touched, and especially if the sensation be attended with pain. This criterion, however, would seem sometimes to be a false one; for occasionally it is the condition of the individual that causes the sensation to be painful. Again, of two things, that is the hotter which the more readily melts a fusible substance, or sets on fire an inflammable one. Again, of two masses of one and the same substance, the larger is said to have more heat than the smaller. Again, of two bodies, that is said to be the [20] hotter which takes the longer time in cooling, as also we call that which is rapidly heated hotter in its nature than that which is long about it—as we call something contrary if it is at a distance, similar if it is nearby. The term hotter is used then in all the various senses that have been mentioned, and perhaps in still more. Now it is impossible for one body to be hotter than another in all these different fashions. [25] Boiling water for instance, though it is more scalding than flame, yet has no power of burning or melting combustible or fusible matter, while flame has. So again this boiling water is hotter than a small fire, and yet gets cold more rapidly and [30] completely. For in fact fire never becomes cold; whereas water invariably does so. Boiling water, again, is hotter to the touch than oil; yet it gets cold and solid more rapidly than this other fluid. Blood, again, is hotter to the touch than either water or oil, and yet coagulates before them. Iron, again, and stones and other similar bodies [35] are longer in getting heated than water, but when once heated burn other substances with a much greater intensity. Another distinction is this. In some of the [649a1] bodies which are called hot the heat is derived from without, while in others it belongs to the bodies themselves; and it makes a most important difference whether the heat has the former or the latter origin. For one of them comes close to being hot [5] accidentally and not in its own right—as if, finding that some man in a fever was a musician, one were to say that musicians are hotter than healthy men. Of that which is hot per se and that which is hot per accidens, the former is the slower to cool, while not rarely the latter is the hotter to the touch. The former again is the [10] more burning of the two—flame, for instance, as compared with boiling water— while the latter, as the boiling water, which is hot per accidens, is the more heating to the touch. From all this it is clear that it is no simple matter to decide which of two bodies is the hotter. For the first may be the hotter in one sense, the second the [15] hotter in another. Indeed in some of these cases it is impossible to say simply even whether a thing is hot or not. For the actual substratum may not itself be hot, but may be hot when coupled with heat as an attribute, as would be the case if one attached a single name to hot water or hot iron. It is after this manner that blood is hot. In such cases—in those, that is, in which the substratum owes its heat to an [20] external influence—it is plain that cold is not a mere privation, but a fact of nature.
There is no knowing but that even fire may be another of these cases. For the substratum of fire may be smoke or charcoal, and though the former of these is always hot, smoke being an uprising vapour, yet the latter becomes cold when it is extinguished, as also would oil and pinewood under similar circumstances. But even [25] substances that have been burnt nearly all possess some heat, cinders, for example, and ashes, the waste-products of animals, and, among the excretions, bile; because some residue of heat has been left in them after their combustion. It is in another sense that pinewood and fat substances are hot; namely, because they rapidly assume the actuality of fire.
[30] Heat appears to cause both coagulation and melting. Now such things as are formed merely of water are solidified by cold, while such as are formed of nothing but earth are solidified by fire. Hot substances again are solidified by cold, and, when they consist chiefly of earth, the process of solidification is rapid, and the resulting substance is insoluble; but, when their main constituent is water, the solid matter is again soluble. What kinds of substances, however, admit of being solidified, and what are the causes of solidification, are questions that have already been dealt with more precisely in another treatise.
Now what is hot and what sort of thing is hotter are determined in a variety of ways, and those features do not belong to everything in the same way: rather, we [649b1] must specify that this substance is hotter per se, though that other is often hotter per accidens; or again, that this substance is potentially hot, that other actually so; or again, that this substance is hotter in the sense of causing a greater feeling of heat when touched, while that other is hotter in the sense of producing flame and [5] burning. The term hot being used in all these various senses, it plainly follows that the term cold will also be used with like multiplicity.
So much then as to hot and cold, hotter and colder.
3 · In natural sequence we have next to treat of dry and moist. These terms [10] are used in various senses. Sometimes, for instance, they denote things that are potentially, at other times things that are actually, dry or moist. Ice for example, or any other solidified fluid, is spoken of as being actually and accidentally dry while potentially and essentially it is moist. Similarly earth and ashes and the like, when mixed with water, are actually and accidentally moist, but potentially and [15] essentially are dry. Now separate the constituents in such a mixture and you have on the one hand the watery components, which take their shape from their container, and these are both actually and potentially moist, and on the other hand the earthy components, and these are all dry; and it is to bodies of this sort that the term ‘dry’ is most properly and absolutely applicable. So also the opposite term ‘moist’ is strictly and absolutely applicable in an analogous way. The same remark applies also to hot bodies and to cold. [20]
These distinctions, then, being laid down, it is plain that blood is hot in one way;7 for it is spoken of as boiling water would be were it denoted by a single term. But the substratum of blood, that which it is while it is blood is not hot. Blood then in a certain sense is essentially hot, and in another sense is not so. For heat is [25] included in the definition of blood, just as whiteness is included in the definition of a white man; but so far as blood becomes hot from some external influence, it is not hot essentially.
As with hot and cold, so also is it with dry and moist. We can therefore understand how some substances are hot and moist so long as they remain in the living body, but become perceptibly cold and coagulate so soon as they are [30] separated from it; while others are hot and consistent while in the body, but when withdrawn undergo a change to the opposite condition, and become cold and moist. Of the former blood is an example, of the latter bile; for while blood solidifies, yellow bile becomes more moist. We must attribute to such substances the possession of opposite properties in a greater or less degree.
In what sense, then, the blood is hot and in what sense fluid, and how far it [650a1] partakes of the opposite properties, has now been fairly explained. Now since everything that grows must take nourishment, and nutriment in all cases consists of moist and dry substances, and since it is by the force of heat that these are [5] concocted and changed, it follows that all living things, animals and plants alike, must on this account, if on no other, have a natural source of heat; and this, like the working of the food,8 must belong to many parts. For first of all there is the mouth [10] and the parts inside the mouth, on which the first share in the duty clearly devolves, in such animals at least as live on food which requires disintegration. The mouth, however, does not actually concoct the food, but merely facilitates concoction; for the subdivision of the food into small bits facilitates the action of heat upon it. After the mouth come the upper and the lower abdominal cavities, and here it is that [15] concoction is effected by the aid of natural heat. Again, just as there is a channel for the admission of the unconcocted food into the stomach, namely the mouth, and in some animals the so-called oesophagus, which is continuous with the mouth and reaches to the stomach, so must there also be other channels by which the nutriment [20] shall pass out of the stomach and intestines into the body at large, and to which these cavities shall serve as a kind of manger. For plants get their food from the earth by means of their roots; and this food is already elaborated when taken in, which is the reason why plants produce no excrement, the earth and its heat serving them in the place of a stomach. But animals, with scarcely an exception, and conspicuously all such as are capable of locomotion, are provided with a stomachal [25] sac, which is as it were an internal substitute for the earth. They must therefore have some instrument which shall correspond to the roots of plants, with which they may absorb their food from this sac, so that the proper end of the successive stages of concoction may be attained. The mouth then, its duty done, passes over the food to the stomach, and there must necessarily be something to receive it in turn from this. This something is furnished by the blood-vessels, which run throughout the [30] whole extent of the mesentery from its lowest part right up to the stomach. A description of these will be found in the Anatomies and in the Natural History. Now as there is a receptacle for the entire matter taken as food, and also a receptacle for its excremental residue, and again a third receptacle, namely the vessels, which serve as such for the blood, it is plain that this blood must be the final [35] nutritive material in such animals as have it; while in bloodless animals the same is the case with the analogous stuff. This explains why the blood diminishes in [650b1] quantity when no food is taken, and increases when much is consumed, and also why it becomes healthy and unhealthy according as the food is of the one or the other character. These facts, then, and others of a like kind, make it plain that the purpose of the blood in sanguineous animals is to subserve the nutrition of the body. They also explain why no more sensation is produced by touching the blood than by [5] touching one of the excretions or the food, whereas when the flesh is touched sensation is produced. For the blood is not continuous nor united by growth with the flesh, but simply lies in its receptacle, that is in the heart and vessels. The manner in which the parts grow at the expense of the blood, and indeed the whole question of [10] nutrition, will find a more suitable place for exposition in the treatise on generation, and in other writings. For our present purpose all that need be said is that the blood exists for the sake of nutrition, that is the nutrition of the parts; and with this much let us therefore content ourselves.
4 · What are called fibres are found in the blood of some animals but not of all. There are none, for instance, in the blood of deer and of roes; and for this reason [15] the blood of such animals as these never coagulates. For one part of the blood consists mainly of water and therefore does not coagulate, this process occurring only in the other and earthy constituent, that is to say in the fibres, while the fluid part is evaporating.
Some at any rate of the animals with watery blood have a keener intellect. This [20] is due not to the coldness of their blood, but rather to its thinness and purity; neither of which qualities belongs to the earthy matter. For the thinner and purer its fluid is, the more easily affected is an animal’s sensibility. Thus it is that some bloodless animals are more intelligent than some among the sanguineous kinds. Such for [25] instance, as already said, is the case with the bee and the tribe of ants, and whatever other animals there may be of a like nature. At the same time too great an excess of water makes animals timorous. For fear chills the body; so that in animals whose heart contains so watery a mixture the way is prepared for the operation of this emotion. For water is congealed by cold. This also explains why bloodless animals [30] are, as a general rule, more timorous than such as have blood, so that they remain motionless, when frightened, and discharge their excretions, and in some instances change colour. Such animals, on the other hand, as have thick and abundant fibres in their blood are of a more earthy nature, and of a choleric temperament, and liable to bursts of passion. For anger is productive of heat; and solids, when they have been made hot, give off more heat than fluids. The fibres therefore, being earthy and [651a1] solid, are turned into so many hot embers in the blood and cause ebullition in the fits of passion.
This explains why bulls and boars are so choleric and so passionate. For their blood is exceedingly rich in fibres, and the bull’s at any rate coagulates more rapidly than that of any other animal. If these fibres are taken out of the blood, it will no [5] longer coagulate; just as the watery residue of mud will not coagulate after removal of the earth—for the fibres consist of earth. But if the fibres are left the fluid coagulates, as also does mud, under the influence of cold. For when the heat is expelled by the cold, the fluid, as has been already stated, passes off with it by [10] evaporation, and the residue is dried up and solidified, not by heat but by cold. So long, however, as the blood is in the body, it is kept fluid by animal heat.
The character of the blood affects both the temperament and the sensory faculties of animals in many ways. This is indeed what might reasonably be expected, seeing that the blood is the material of which the whole body is made. For nutriment supplies the material, and the blood is the ultimate nutriment. It makes [15] then a considerable difference whether the blood be hot or cold, thin or thick, turbid or clear.
The watery part of the blood is serum; and it is watery, either owing to its not being yet concocted, or owing to its having become corrupted; so that one part of the serum is the resultant of a necessary process, while another part is for the sake of the blood.
[20] 5 · The differences between lard and suet correspond to differences of blood. For both are blood concocted into these forms as a result of abundant nutrition, being that surplus blood that is not expended on the fleshy part of the body, and is of an easily concocted and well-nourished character. This is shown by the greasiness of [25] these substances; for such grease in fluids is due to a combination of air and fire. It follows from what has been said that no non-sanguineous animals have either lard or suet; for they have no blood. Among sanguineous animals those whose blood is dense have suet rather than lard. For suet is of an earthy nature, that is to say, it contains but a small proportion of water and is chiefly composed of earth; and this it is that makes it coagulate, just as the fibrous matter of blood coagulates, or broths [30] which contain such fibrous matter. Thus it is that non-ambidentate horned animals possess suet. For the very fact that they have horns and huckle-bones shows that their composition is rich in this earthy element; for all such appurtenances are solid and earthy in character. On the other hand in those hornless animals that are [35] ambidentate and possess toes, there is no suet, but in its place lard; and this, not being of an earthy character, neither coagulates nor splits when it dries.
Both lard and suet when present in moderate amount are beneficial; for they [651b1] contribute to health and strength, while they are no hindrance to sensation. But when they are present in great excess, they are injurious and destructive. For were the whole body formed of them it would perish. For an animal is an animal in virtue [5] of its sensory part, that is in virtue of its flesh, or of the substance analogous to flesh. But the blood, as before stated, is not sensitive; as therefore is neither lard nor suet, seeing that they are concocted blood. Were then the whole body composed of these substances, it would be utterly without sensation. Such animals, again, as are [10] excessively fat age rapidly. For so much of their blood is used in forming fat, that they have but little left; and when there is but little blood the way is already open for decay. For decay may be said to be deficiency of blood, the scantiness of which renders it liable, like all bodies of small bulk, to be affected by any chance excess of heat or cold. For the same reason fat animals are less fertile than others. For that [15] part of the blood which should go to form semen and seed is used up in the production of lard and suet, which are nothing but concocted blood; so that in these animals there is either no residue at all, or only a scanty amount.
6 · So much then for blood and serum, and for lard and suet. Each of these, and their causes, have been described.
[20] The marrow also is of the nature of blood, and not, as some think, the germinal force of the semen. That this is the case is quite evident in very young animals. For [25] in the embryo the marrow of the bones has a blood-like appearance, which is but natural, seeing that the parts are all constructed out of blood, and that it is on blood that the embryo is nourished. But, as the young animal grows up and ripens into maturity, the marrow changes its colour, just as do the parts and the viscera. For the viscera also in animals, so long as they are young, have each and all a blood-like look, owing to the large amount of this fluid which they contain.
In those animals which contain lard, the marrow is greasy and lard-like; but when the blood is converted by concoction into suet, and does not assume the form [30] of lard, then the marrow also has a suety character. In those animals, therefore, that have horns and are not ambidentate, the marrow has the character of suet; while it takes the form of lard in those that are ambidentate and have the foot divided into toes. What has been said hardly applies to the spinal marrow. For it is necessary that this shall be continuous and extend without break through the whole backbone, inasmuch as this bone consists of separate vertebrae. But were the spinal marrow either greasy or of suet, it could not hold together in such a continuous mass as it [35] does, but would either be too fluid or too frangible.
There are some animals that can hardly be said to have any marrow. These are those whose bones are strong and solid, as is the case with the lion. For in this animal the marrow is so utterly insignificant that the bones look as though they had [652a1] none at all. However, as it is necessary that animals shall have bones or something analogous to them, such as the fish-spines of water-animals, it is also a matter of necessity that some of these bones shall contain marrow; for the substance [5] contained within the bones is the nutriment out of which these are formed. Now the universal nutriment, as already stated, is blood; and it is reasonable that marrow should be suety or fatty. For the blood within the bone, owing to the heat which is developed in it from its being thus surrounded, undergoes concoction, and self-concocted blood is suet or lard. So also it is easy to understand why, in those animals [10] that have strong and compact bones, some of these should be entirely void of marrow, while the rest contain but little of it; for here the nutriment is spent in forming the bones.
Those animals that have fish-spines in place of bones have no other marrow than that of the backbone. For in the first place they have naturally but a small amount of blood; and secondly the only hollow fish-spine is that of the backbone. In [15] this then marrow is formed; this being the only spine in which there is space for it, and, moreover, being the only one which owing to its division into parts requires a connecting bond. This too is the reason why the marrow here, as already mentioned, is somewhat different from that of other bones. For, having to act the part of a clasp, it must be of glutinous character and at the same time sinewy so as to admit of stretching.
Such then are the reasons for the existence of marrow, in those animals that [20] have any, and such its nature. It is evidently the surplus of the sanguineous nutriment apportioned to the bones and fish-spines, which has undergone concoction owing to its being enclosed within them.
7 · From the marrow we pass on in natural sequence to the brain. For there are many who think that the brain itself consists of marrow, and that it forms the [25] commencement of that substance, because they see that the spinal marrow is continuous with it. In reality the two may be said to be utterly opposite to each other in character. For of all the parts of the body there is none so cold as the brain; whereas the marrow is of a hot nature, as is plainly shown by its fat and greasy [30] character. Indeed this is the very reason why the brain and spinal marrow are continuous with each other. For, wherever the action of any part is in excess, nature so contrives as to set by it another part with an excess of contrary action, so that the excesses of the two may counterbalance each other. Now that the marrow is hot is [35] clearly shown by many indications. The coldness of the brain is also manifest enough even to the touch; and, secondly, of all the fluid parts of the body it is the driest and the one that has the least blood; for in fact it has no blood at all in its [652b1] proper substance. Thus brain is not residual matter, nor yet is it one of the parts which are continuous with each other; but it has a character peculiar to itself, as might indeed be expected. That it has no continuity with the organs of sense is plain [5] from simple inspection, and is still more clearly shown by the fact, that, when it is touched, no sensation is produced; in which respect it resembles the blood of animals and their excrement. The purpose of its presence in animals is no less than the preservation of the whole body. For some writers assert that the soul is fire or some such force. This, however, is but a crude assertion; and it would perhaps be better to say that the soul is incorporate in some substance of a fiery character. The [10] reason for this being so is that of all substances there is none so suitable for ministering to the operations of the soul as that which is possessed of heat. For nutrition and the imparting of motion are offices of the soul, and it is by heat that these are most readily effected. To say then that the soul is fire is much the same thing as to confound the auger or the saw with the carpenter or his craft, simply [15] because the work is done when the two are near one another. So far then this much is plain, that all animals must necessarily have a certain amount of heat. But as all influences require to be counterbalanced, so that they may be reduced to moderation and brought to the mean (for in the mean, and not in either extreme, lies their [20] substance and account), nature has contrived the brain as a counterpoise to the region of the heart with its contained heat, and has given it to animals to moderate the latter, combining in it the properties of earth and water. For this reason it is, that every sanguineous animal has a brain; whereas no bloodless creature has such [25] an organ, unless indeed it be, as the octopus, by analogy. For where there is no blood, there in consequence is but little heat. The brain, then, tempers the heat and seething of the heart. In order, however, that it may itself have a moderate amount of heat, branches run from both blood-vessels, that is to say from the great vessel [30] and from what is called the aorta, and end in the membrane which surrounds the brain; while at the same time, in order to prevent any injury from the heat, these encompassing vessels, instead of being few and large, are numerous and small, and their blood scanty and clear, instead of being turbid and thick. We can now [35] understand why fluxes have their origin in the head, and occur whenever the parts about the brain have more than a due proportion of coldness. For when the [653a1] nutriment steams upwards through the blood-vessels, its refuse portion is chilled by the influence of this region, and forms fluxes of phlegm and serum. We must suppose, to compare small things with great, that the like happens here as occurs in [5] the production of showers. For when vapour steams up from the earth and is carried by the heat into the upper regions, so soon as it reaches the cold air that is above the earth, it condenses again into water owing to the refrigeration, and falls back to the earth as rain. These, however, are matters which may be suitably considered in the Principles of Diseases, so far as natural philosophy has anything to say to them. [10]
It is the brain again—or, in animals that have no brain, the part analogous to it—which is the cause of sleep. For either by chilling the blood that streams upwards after food, or by some other similar influences, it produces heaviness in the region in which it lies (which is the reason why drowsy persons hang the head), and [15] causes the heat to escape downwards in company with the blood. It is the accumulation of this in excess in the lower region that produces sleep, taking away the power of standing upright from those animals to whom that posture is natural, and from the rest the power of holding up the head. These, however, are matters which have been separately considered in the treatises on Sensation and on Sleep. [20] That the brain is a compound of earth and water is shown by what occurs when it is boiled. For, when so treated, it turns hard and dry, inasmuch as the water is evaporated by the heat, and leaves the earthy part behind. Just the same occurs when pulse and other fruits are boiled. For these also are hardened and become altogether earthy, because the water which enters into their composition is driven off and leaves the earth, which is their main constituent, behind. [25]
Of all animals, man has the largest brain in proportion to his size; and it is larger in men than in women. This is because the region of the heart and of the lung is hotter and richer in blood. This again explains why man, alone of animals, stands [30] erect. For the heat, overcoming any opposite inclination, makes growth take its own line of direction, which is from the centre of the body upwards. It is then as a counterpoise to his excessive heat that there is this superabundant fluidity and coldness; and it is again owing to this superabundance that the cranial bone which some call the bregma is the last to become solidified; so long does evaporation [35] continue to occur through it under the influence of heat. Man is the only sanguineous animal in which this takes place. Man, again, has more sutures in his skull than any other animal, and the male more than the female. The explanation [653b1] is again to be found in the greater size of the brain, which demands free ventilation, proportionate to its bulk. For if the brain be either too moist or too dry, it will not perform its office, but in the one case will freeze the blood, and in the other will not cool it at all; and thus will cause disease, madness, and death. For the cardiac heat [5] and the centre of life is most delicate in its sympathies, and is immediately sensitive to the slightest change or affection of the blood on the outer surface of the brain.
The fluids which are present in the animal body from the first have now nearly all been considered. Amongst those that appear only at a later period are the residua [10] of the food, which include the deposits of the belly and also those of the bladder. Besides these there is the semen and the milk, in those animals which are of such a nature as to have them. Of these fluids, the excremental residua of the food may be suitably discussed by themselves, when we come to examine and consider the subject of nutrition. Then will be the proper time to explain in what animals they [15] are found, and what are the reasons for their presence. Similarly all questions concerning the semen and the milk may be dealt with in the treatise on Generation, for the former of these fluids is the very starting-point of the generative process, and the latter exists for the sake of generation.
8 · We have now to consider the remaining homogeneous parts, and will [20] begin with flesh, and with the substance that, in animals that have no flesh, takes its place. The reason for so beginning is that flesh forms in animals both a principle and a body in itself. Its right to this precedence can also be demonstrated logically. For an animal is by our definition something that has sensibility and chief of all the primary sensibility, which is that of touch; and it is the flesh, or analogous [25] substance, which is the organ of this sense—either the primary organ, in the same way as the pupil is the organ of sight, or it is the organ and the medium through which the object acts combined, comparable to the pupil with the whole transparent medium attached to it. Now in the case of the other senses it was impossible for nature to unite the medium with the sense-organ, nor would such a junction have served any purpose; but in the case of touch she was compelled by necessity to do so. For of all the sense-organs that of touch is the only one that has corporeal substance, [30] or at any rate it is more corporeal than any other.
It is obvious also to sense that it is for the sake of this that all the other parts exist. By the other parts I mean the bones, the skin, the sinews, and the blood-vessels, and, again, the hair and the various kinds of nails, and anything else there may be of a like character. Thus the bones are a contrivance to give security to [35] the soft parts, to which purpose they are adapted by their hardness; and in animals that have no bones the same office is fulfilled by some analogous substance, as by fish-spine in some fishes, and by cartilage in others.
Now in some animals this supporting substance is situated within the body, [654a1] while in some of the bloodless species it is placed on the outside. The latter is the case in all the Crustacea, as the crabs and the crayfish; it is the case also in the Testacea, as for instance in the several species known by the general name of oysters. For in all these animals the fleshy substance is within, and the earthy matter, which holds the soft parts together and keeps them from injury, is on the [5] outside. For the shell not only enables the soft parts to hold together, but also, as the animal is bloodless and so has but little natural warmth, surrounds it, as a chaufferette does the embers, and keeps in the smouldering heat. Similar to this seems to be the arrangement in another kind of animals, namely the tortoises and [10] the several kinds of water-tortoise. But in Insects and in Cephalopods the plan is entirely different, there being moreover a contrast between these two themselves. For in neither of these does there appear to be any bony or earthy part, worthy of notice, distinctly separated from the rest of the body. Thus in the Cephalopods the main bulk of the body consists of a soft flesh-like substance, or rather of a substance [15] which is intermediate between flesh and sinew, so as not to be so readily destructible as actual flesh. For it is soft like flesh, while it admits of stretching like the sinew. It splits not longitudinally, but into circular segments, like flesh, this being the most advantageous condition, so far as strength is concerned. These animals have also a part inside them corresponding to the spinous bones of fishes. For instance, in the [20] cuttle-fishes there is what is known as the pounce, and in the calamaries there is the so-called pen. In the octopus, on the other hand, there is no such internal part, because the body, or, as it is termed in them, the head, forms but a short sac, whereas it is of considerable length in the other two; and it was this length which led nature to assign to them their hard support, so as to ensure their straightness and [25] inflexibility; just as she has assigned to sanguineous animals their bones or their fish-spines, as the case may be. To come now to Insects. In these the arrangement is quite different from that of the Cephalopods and from that which obtains in sanguineous animals, as indeed has been already stated. For in an insect there is no distinction into soft and hard parts, but the whole body is hard, the hardness, however, being of such a character as to be more flesh-like than bone, and more earthy and bone-like than flesh. The purpose of this is to make the body of the insect [30] less liable to get broken into pieces.
9 · There is a resemblance between the osseous and the vascular systems; for each has a central part in which it begins, and each forms a continuous whole. For no bone in the body exists as a separate thing in itself, but each is either a portion of [35] what may be considered a continuous whole, or at any rate is linked with the rest by contact and by attachments; so that nature may use adjoining bones either as though they were actually continuous and formed a single bone, or, for purposes of [654b1] flexure, as though they were two and distinct. And similarly no blood-vessel has in itself a separate individuality; but they all form parts of one whole. For an isolated bone, if such there were, would in the first place be unable to perform the office for the sake of which bones exist; for, were it discontinuous and separated from the rest [5] by a gap, it would be perfectly unable to produce either flexure or extension; nor only so, but it would actually be injurious, acting like a thorn or an arrow lodged in the flesh. Similarly if a vessel were isolated, and not continuous with the vascular origin, it would be unable to retain the blood within it in a proper state. For it is the warmth derived from this origin that hinders the blood from coagulating; indeed the [10] blood, when withdrawn from its influence, becomes manifestly putrid. Now the origin of the blood-vessels is the heart, and the origin of the bones, in all animals that have bones, is what is called the backbone. With this all the other bones of the body are in continuity; for it is the backbone that holds together the whole length of an animal and preserves its straightness. But since it is necessary that the body of an [15] animal shall bend during locomotion, this is one in virtue of the continuity of its parts, yet by its division into vertebrae is made to consist of many segments. It is from this that the bones of the limbs, in such animals as have these parts, proceed, and with it they are continuous, some having their extremities adapted to each [20] other, either by the one being hollowed and the other rounded, or by both being hollowed and including between them a hucklebone, as a connected bolt, so as to allow of flexure and extension. For without some such arrangement these movements would be utterly impossible, or at any rate would be performed badly. There are some joints, again, in which the lower end of the one bone and the upper end of [25] the other are alike in shape; and cartilaginous pieces are interposed in the joint, to serve as a kind of padding, and prevent the two extremities from grating against each other.
Round about the bones, and attached to them by thin fibrous bands, grow the fleshy parts, for the sake of which the bones themselves exist. For just as an artist, [30] when he is moulding an animal out of clay or other soft substance, takes first some solid body as a basis, and round this moulds the clay, so also has nature acted in fashioning the animal body out of flesh. Thus we find all the fleshy parts, with one exception, supported by bones, which serve, when the parts are organs of motion, to facilitate flexure, and, when the parts are motionless, act as a protection. The ribs, [655a1] for example, which enclose the chest are intended to ensure the safety of the heart and neighbouring viscera. The exception is the belly. The walls of this are in all animals devoid of bones; in order that there may be no hindrance to the expansion which necessarily occurs in this part after a meal, nor, in females, any interference with the growth of the foetus, which is lodged here.
[5] Now the bones of viviparous animals, of such, that is, as are not merely externally but also internally viviparous, vary but very little from each other in point of strength. For they are all much greater, in proportion to the size of their bodies, than the non-viviparous animals. For in some places many Vivipara grow to [10] an enormous size, as is the case in Libya and in hot and dry countries generally. But the greater the bulk of an animal, the stronger, the bigger, and the harder, are the supports which it requires; and this requirement will be most marked in those that live a life of rapine. Thus it is that the bones of males are harder than those of females; and the bones of flesh-eaters, that get their food by fighting, are harder [15] than those of others. Of this the lion is an example; for so hard are its bones, that, when struck, they give off sparks, as though they were stones. It may be mentioned also that the dolphin, inasmuch as it is viviparous, is provided with bones and not with fish-spines.
In those sanguineous animals, on the other hand, that are not viviparous, the bones present successive slight variations of character. Thus in birds there are bones, but these are not so strong as the bones of the Vivipara. Then come the [20] oviparous fishes, where there is fish-spine. In the serpents too the bones have the character of fish-spine, excepting in the very large species, where the solid foundation of the body requires to be stronger, in order that the animal itself may be strong, the same reason prevailing as in the case of the Vivipara. Lastly, in the Selachia, as they are called, the fish-spines are replaced by cartilage. For it is necessary that the movements of these animals shall be of an undulating character; [25] and this again requires the framework that supports the body to be made of a pliable and not of a brittle substance. Moreover, nature has used all the earthy matter on the skin; and she is unable to allot to many different parts one and the same superfluity of material. Even in viviparous animals many of the bones are cartilaginous. This happens in those parts where it is to the advantage of the [30] surrounding flesh that its solid base shall be soft and mucilaginous. Such, for instance, is the case with the ears and nostrils; for in projecting parts brittle substances would soon get broken. Cartilage and bone are indeed fundamentally the same thing, the differences between them being merely matters of degree. Thus neither cartilage nor bone, when once cut off, grows again. Now the cartilages of these land animals are without marrow, that is without any distinctly separate [35] marrow. For the marrow, which in bones is distinctly separate, is here mixed up with the whole mass, and gives a soft and mucilaginous consistence to the cartilage. But in the Selachia the backbone, though it is cartilaginous, yet contains marrow; [655b1] for here it stands in the stead of a bone.
Very nearly resembling the bones to the touch are such parts as nails, hoofs, claws, horns, and the beaks of birds, all of which are intended to serve as means of [5] defence. For the organs which are made out of these substances, and which are called by the same names as the substances themselves, the organ hoof, for instance, and the organ horn, are contrivances to ensure the preservation of the animals to which they severally belong. In this class too must be reckoned the teeth, which in some animals have but a single function, namely the mastication of the food, while [10] in others they have an additional office, namely to serve as weapons; as is the case with all animals that have sharp interfitting teeth or that have tusks. All these parts are necessarily of a solid and earthy character; for the value of a weapon depends on such properties. Hence it is that all such parts are more developed in four-footed vivipara than in man. For there is always more earth in the composition of these [15] animals than in that of the human body. However, not only all these parts but such others as are nearly connected with them, skin for instance, bladder, membrane, hairs, feathers, and their analogues, and any other similar parts that there may be, will be considered farther on with the heterogeneous parts. There we shall inquire into the causes which produce them, and into the goals of their presence severally in [20] the bodies of animals. For, as with the heterogeneous parts, so with these, it is from a consideration of their functions that alone we can derive any knowledge of them. The reason for dealing with them at all in this part of the treatise, and classifying them with the homogeneous parts, is that both the organs and their parts have the same name; and of all these substances flesh and bone form the basis. Semen and milk were also passed over when we were considering the homogeneous fluids. For [25] the treatise on Generation affords a more suitable place for their examination, seeing that the former of the two is a principle of the thing generated, while the latter is its nourishment.
10 · Let us now make, as it were, a fresh beginning, and consider the heterogeneous parts, taking those first which are the first in importance. For in all animals, at least in all the perfect kinds, there are two parts more essential than the [30] rest, namely the part which serves for the ingestion of food, and the part which serves for the discharge of its residue. For without food growth and even existence is impossible. (As for plants, though they also are included by us among things that have life, yet are they without any part for the discharge of waste residue. For the food which they absorb from the ground is already concocted, and they give off [35] instead their seeds and fruits.) And in all there is a third part, intermediate between these two, in which is situated the principle of life. Plants, again, inasmuch as they [656a1] are without locomotion, present no great variety in their heterogeneous parts. For, where the functions are but few, few also are the organs required to effect them. The configuration of plants is a matter then for separate consideration. Animals, however, that not only live but perceive, present a greater multiformity of parts, and [5] this diversity is greater in some animals than in others, being most varied in those to whose share has fallen not mere life but life of high degree. Now such an animal is man. For of all living beings with which we are acquainted man alone partakes of the divine, or at any rate partakes of it in a fuller measure than the rest. For this [10] reason, then, and also because his external parts and their forms are more familiar to us than those of other animals, we must speak of man first; and this the more fitly, because in him alone do the natural parts hold the natural position; his upper part being turned towards that which is upper in the universe. For, of all animals, man alone stands erect.
In man, then, the head is destitute of flesh; this being the necessary [15] consequence of what has already been stated concerning the brain. There are, indeed, some who hold that the life of man would be longer than it is, were his head more abundantly furnished with flesh; and they account for the absence of this substance by saying that it is intended to add to the perfection of sensation. For the brain they assert to be the organ of sensation; and sensation, they say, cannot penetrate to parts that are too thickly covered with flesh. But neither part of this [20] statement is true. On the contrary, were the region of the brain thickly covered with flesh, the very purpose for which animals are provided with a brain would be directly contravened. For the brain would itself be heated to excess and so unable to cool any other part. Again, the brain cannot be the cause of any of the sensations, [25] seeing that it is itself as utterly without feeling as any one of the excretions. These writers see that certain of the senses are located in the head, and are unable to discern the reason for this; they see also that the brain is the most peculiar of all the animal organs; and out of these facts they form an argument, by which they link sensation and brain together. It has, however, already been clearly set forth in the treatise on Sensation, that it is the region of the heart that constitutes the sensory centre. There also it was stated that two of the senses, namely touch and taste, are [30] manifestly in immediate connexion with the heart; and that as regards the other three, namely hearing, sight, and the centrally placed sense of smell, it is the character of their sense-organs which causes them to be lodged as a rule in the head. Vision is so placed in all animals. But such is not invariably the case with hearing or [35] with smell. For fishes and the like hear and smell, and yet have novisible organs for these senses in the head; a fact which demonstrates the accuracy of the opinion here maintained. Now that vision, whenever it exists, should be in the neighbourhood of [656b1] the brain is but what one would rationally expect. For the brain is moist and cold, and vision is of the nature of water, water being of all transparent substances the one most easily confined. Moreover it cannot but necessarily be that the more precise senses will have their precision rendered still greater if ministered to by [5] parts that have the purest blood. For the motion of the heat of blood destroys sensory activity. For these reasons the organs of these senses are lodged in the head.
It is not only the fore part of the head that is destitute of flesh, but the hind part also. For, in all animals that have a head, it is this head which more than any other part requires to be held up. But, were the head heavily laden with flesh, this would be impossible; for nothing so burdened can be held upright. This is an additional [10] proof that the absence of flesh from the head is not for the sake of brain sensation. For there is no brain in the hinder part of the head, and yet this is as much without flesh as is the front.
In some animals hearing as well as vision is lodged in the region of the head. [15] Nor is this without a rational explanation. For what is called the empty space is full of air, and the organ of hearing is, as we say, of the nature of air. Now there are channels which lead from the eyes to the blood-vessels that surround the brain; and similarly there is a channel which leads back again from each ear and connects it with the hinder part of the head. [But no part that is without blood is endowed with sensation, as neither is the blood itself, but only some one of the parts that are [20] formed of blood. That is why in the Sanguinea no bloodless part is capable of sensation, nor is the blood itself; for it is no part of the animals.]9
The brain in all animals that have one is placed in the front part of the head; because the direction in which sensation acts is in front; and because the heart, from which sensation proceeds, is in the front part of the body; and lastly because the [25] instruments of sensation are the blood-containing parts, and the cavity in the posterior part of the skull is destitute of blood-vessels.
As to the position of the sense-organs, they have been arranged by nature in the following well-ordered manner. The organs of hearing are so placed as to divide the circumference of the head into two equal halves; for they have to hear not only sounds which are directly in a line with themselves, but sounds from all quarters. The organs of vision are placed in front, because sight is exercised only in a straight [30] line, and moving as we do in a forward direction it is necessary that we should see before us, in the direction of our motion. Lastly, the organs of smell are placed with good reason between the eyes. For as the body consists of two parts, a right half and a left, so also each organ of sense is double. In the case of touch this is not apparent, [35] the reason being that the primary organ of this sense is not the flesh or analogous part, but lies internally. In the case of taste, which is merely a modification of touch [657a1] and which is placed in the tongue, the fact is more apparent than in the case of touch, but still not so manifest as in the case of the other senses. However, even in taste it is evident enough; for in some animals the tongue is plainly forked. The double character of the sensations is, however, more conspicuous in the other organs of sense. For there are two ears and two eyes, and the nostrils, though joined together, are also two. Were these latter otherwise disposed, and separated from [5] each other as are the ears, neither they nor the nose in which they are placed would be able to perform their office. For in such animals as have nostrils olfaction is effected by means of inspiration, and the organ of inspiration is placed in front and in the middle line. This is the reason why nature has brought the two nostrils together and placed them as the central of the three sense-organs, setting them side by side on a level with each other, to avail themselves of the inspiratory motion. In [10] other animals than man the arrangement of these sense-organs is also such as is adapted in each case to the special requirements.
11 · For instance, in quadrupeds the ears stand out freely from the head and are set to all appearance above the eyes. Not that they are in reality above the eyes; [15] but they seem to be so, because the animal does not stand erect, but has its head hung downwards. This being the usual attitude of the animal when in motion, it is of advantage that its ears shall be high up and movable; for by turning themselves about they can the better take in sounds from every quarter.
12 · In birds, on the other hand, there are only the auditory passages. This is [20] because their skin is hard and because they have feathers instead of hairs, so that they have not got the proper material for the formation of ears. Exactly the same is the case with such oviparous quadrupeds as are clad with scaly plates, and the same explanation applies to them. There is also one of the vivipara, namely the seal, that has no ears but only the auditory passages. The explanation of this is that the seal is a deformed quadruped.
[25] 13 · Men, and Birds, and Quadrupeds, viviparous and oviparous alike, have their eyes protected by lids. In the Vivipara there are two of these; and both are used also in the act of blinking; whereas the oviparous quadrupeds, and the heavy-bodied [30] birds as well as some others, use only the lower lid to close the eye; while birds blink by means of a membrane that issues from the corner of the eye. The reason for the eyes being thus protected is that they are of fluid consistency, in order to ensure keenness of vision. For had they been covered with hard skin, they would, it is true, have been less liable to get injured by anything falling into them from without, but they would not have been sharp-sighted. It is then to ensure keenness of vision that [35] the skin over the pupil is fine and delicate; while the lids are for protection from injury. It is as a still further safeguard that all these animals blink, and man most of [657b1] all; this action (which is not performed from deliberate intention but from a natural instinct) serving to keep objects from falling into the eyes; and being more frequent in man than in the rest of these animals, because of the greater delicacy of his skin. These lids are made of a roll of skin; and it is because they are made of skin and contain no flesh that neither they, nor the foreskin, unite again when once cut.
[5] As to the oviparous quadrupeds, and such birds as close the eye with the lower lid, it is the hardness of the skin of their heads which makes them do so. For such birds as have heavy bodies are not made for flight; and so the materials which would otherwise have gone to increase the growth of the feathers are diverted thence, and [10] used to augment the thickness of the skin. Birds therefore of this kind close the eye with the lower lid; whereas pigeons and the like use both. Oviparous quadrupeds are covered with scaly plates; and these in all their forms are harder than hairs, so that the skin also to which they belong is harder than the skin of hairy animals. In these animals, then, the skin on the head is hard, and so does not allow of the formation of [15] an upper eyelid, whereas lower down the integument is of a flesh-like character, so that the lower lid can be thin and extensible.
The act of blinking is performed by the heavy-bodied birds by means of the membrane already mentioned, and not by this lower lid. For in blinking rapid motion is required, and such is the motion of this membrane, whereas that of the lower lid is slow. It is from the corner of the eye that is nearest to the nostrils that the membrane comes. For it is better to have one starting-point than two; and in these [20] birds this starting-point is the junction of eye and nostrils, an anterior starting-point being preferable to a lateral one. Oviparous quadrupeds do not blink in like manner as the birds; for, living as they do on the ground, they are free from the necessity of having eyes of fluid consistency and of keen sight, whereas these are essential requisites for birds, inasmuch as they have to use their eyes at long distances. This [25] too explains why birds with talons, that have to search for prey by eye from aloft, and therefore soar to greater heights than other birds, are sharp-sighted; while common fowls and the like, that live on the ground and are not made for flight, have no such keenness of vision. For there is nothing in their mode of life which imperatively requires it.
Fishes and Insects and the hard-skinned Crustacea present certain differences [30] in their eyes, but none of them have eyelids. As for the hard-skinned Crustacea it is utterly out of the question that they should have any; for an eyelid, to be of use, requires the action of the skin to be rapid. These animals then have hard eyes in [35] default of this protection, just as though the lid were attached to the surface of the eye, and the animal saw through it. Inasmuch, however, as such hardness must necessarily blunt the sharpness of vision, nature has endowed the eyes of Insects, and still more those of Crustacea, with mobility (just as she has given some [658a1] quadrupeds movable ears), in order that they may be able to turn to the light and catch its rays, and so see more plainly. Fishes, however, have eyes of a fluid consistency. For animals that move much about have to use their vision at [5] considerable distances. For land animals, the air is transparent enough. But the water in which fishes live is a hindrance to sharp sight, though it has this advantage over the air, that it does not contain so many objects to knock against the eyes. For this reason, nature, which makes nothing in vain, has given no eyelids to fishes, while to counterbalance the opacity of the water she has made their eyes of fluid [10] consistency.
14 · All animals that have hairs on the body have lashes on the eyelids; but birds and animals with scale-like plates, being hairless, have none. The Libyan ostrich, indeed, is furnished with eyelashes. This exception, however, will be [15] explained hereafter. Of hairy animals, man alone has lashes on both lids. For in quadrupeds there is a greater abundance of hair on the back than on the under side of the body; whereas in man the contrary is the case, and the hair is more abundant on the front surface than on the back. The reason for this is that hair is intended to serve as a protection to its possessor. Now, in quadrupeds the back requires more protection, and their underside, though more noble is smooth because of their [20] inclined posture. But in man, owing to his upright attitude, the anterior and posterior surfaces of the body are on an equality as regards need of protection. Nature therefore has assigned the protective covering to the nobler of the two surfaces; for invariably she brings about the best arrangement of such as are [25] possible. This then is the reason that there is no lower eyelash in any quadruped; though in some a few scattered hairs sprout out under the lower lid. This also is the reason that they never have hair in the armpits, nor on the pubes, as man has. Their hair, then, instead of being collected in these parts, is either thickly set over the whole dorsal surface, as is the case for instance in dogs, or, sometimes, forms a [30] mane, as in horses and the like, or as in the male lion, where the mane is still more ample. So, again, whenever there is a tail of any length, nature decks it with hair, with long hair if the stem of the tail be short, as in horses, with short hair if the stem [35] be long, regard also being had to the condition of the rest of the body. For nature invariably gives to one part what she subtracts from another. Thus when she has covered the general surface of an animal’s body with an excess of hair, she leaves a [658b1] deficiency in the region of the tail. This, for instance, is the case with bears.
No animal has so much hair on the head as man. This, in the first place, is the necessary result of the fluid character of his brain, and of the presence of so many sutures in his skull. For wherever there is the most fluid and the most heat, there [5] also must necessarily occur the greatest outgrowth. But, secondly, in order to protect the head, by preserving it from excess of either heat or cold. And as the brain of man is larger and more fluid than that of any other animal, it requires a proportionately greater amount of protection. For the more fluid a substance is, the more readily does it get excessively heated or excessively chilled, while substances [10] of an opposite character are less liable to such affections.
These, however, are matters which by their close connexion with eyelashes have led us to digress from our real topic, namely the cause to which these lashes owe their existence. We must therefore defer any further remarks we may have to make on these matters till the proper occasion arises.
[15] 15 · Both eyebrows and eyelashes exist for the protection of the eyes; the former that they may shelter them, like the eaves of a house, from any fluids that trickle down from the head; the latter to act like the palisades which are sometimes placed in front of enclosures, and keep out any objects which might otherwise get in. The brows are placed over the junction of two bones, which is the reason that in old [20] age they often become so bushy as to require cutting. The lashes are set at the terminations of small blood-vessels. For the vessels come to an end where the skin itself terminates; and, in all places where these endings occur, the exudation of [25] moisture of a corporeal character actually necessitates the growth of hairs, unless there be some operation of nature which interferes, by diverting the moisture to another purpose.
16 · Viviparous quadrupeds, as a rule, present no great variety of form in the [30] organ of smell. In those of them, however, whose jaws project forwards and taper to a narrow end, so as to form what is called a snout, the nostrils are placed in this projection, there being no other available plan; while, in the rest, there is a more definite demarcation between nostrils and jaws. But in no animal is this part so [35] peculiar as in the elephant, where it attains an extraordinary size and strength. For the elephant uses its nostril as a hand; this being the instrument with which it conveys food, fluid and solid alike, to its mouth. With it, too, it tears up trees, coiling [659a1] it round their stems. In fact it applies it generally to the purposes of a hand. For the elephant has the double character of a land animal, and of one that lives in swamps. Seeing then that it has to get its food from the water, and yet must necessarily breathe, inasmuch as it is a land animal and has blood; seeing, also, that its [5] excessive weight prevents it from passing rapidly from water to land, as some other sanguineous vivipara that breathe can do, it becomes necessary that it shall be suited alike for life in the water and for life on dry land. Just then as divers are sometimes provided with instruments for respiration, through which they can draw air from above the water, and thus may remain for a long time under the sea, so also [10] have elephants been furnished by nature with their lengthened nostril; and, whenever they have to traverse the water, they lift this up above the surface and breathe through it. For the elephant’s trunk, as already said, is a nostril. Now it [15] would have been impossible for this nostril to have such a form had it been hard and incapable of bending. For its very length would then have prevented the animal from supplying itself with food, being as great an impediment as the horns of certain oxen, that are said to be obliged to walk backwards while they are grazing. It is [20] therefore soft and flexible, and, being such, is made, in addition to its own proper functions, to serve the office of the fore-feet; nature in this following her wonted plan of using one and the same part for several purposes. For in polydactylous quadrupeds the fore-feet are intended not merely to support the weight of the body, [25] but to serve as hands. But in elephants, though they must be reckoned polydactylous, as their foot has neither cloven nor solid hoof, the fore-feet, owing to the great size and weight of the body, are reduced to the condition of mere supports; and indeed their slow motion and unfitness for bending make them useless for any other purpose. A nostril, then, is given to the elephant for respiration, as to every other [30] animal that has a lung, and is lengthened out and endowed with its power of coiling because the animal has to remain for considerable periods of time in the water, and is unable to pass thence to dry ground with any rapidity. But as the feet are shorn of their full office, this same part is also, as already said, made by nature to supply [35] their place, and give such help as otherwise would be rendered by them.
As to other sanguineous animals, the birds, the serpents, and the oviparous [659b1] quadrupeds, in all of them there are the nostril-holes, placed in front of the mouth; but in none are there any distinctly formed nostrils, nothing in fact which can be called nostrils except from a functional point of view. A bird at any rate has nothing which can properly be called a nose. For its so-called beak is a substitute for jaws. [5] The reason for this is to be found in the natural conformation of birds. For they are winged bipeds; and this makes it necessary that their head and neck shall be of light weight; just as it makes it necessary that their breast shall be narrow. The beak therefore is formed of a bone-like substance, in order that it may serve as a weapon [10] as well as for nutritive purposes, but is made of narrow dimensions to suit the small size of the head. In this beak are placed the olfactory passages. But there are no nostrils; for such could not possibly be placed there.
As for those animals that have no respiration, it has already been explained [15] why it is that they are without nostrils, and perceive odours either through gills, or through a blow-hole, or, if they are insects, by the hypozoma; and how the power of smelling depends, like their motion, upon the innate breath of their bodies, which in all of them is implanted by nature and not introduced from without.
[20] Under the nostrils are the lips, in such sanguineous animals, that is, as have teeth. For in birds, as already has been said, the purposes of nutrition and defence are fulfilled by a bone-like beak, which forms a compound substitute for teeth and [25] lips. For supposing that one were to cut off a man’s lips, unite his upper teeth together, and similarly his under ones, and then were to lengthen out the two separate pieces thus formed, narrowing them on either side—then we should at once have a bird-like beak.
The use of the lips in all animals except man is to preserve and guard the teeth; [30] and thus it is that the distinctness with which the lips are formed is in direct proportion to the degree of nicety and perfection with which the teeth are fashioned. In man the lips are soft and flesh-like and capable of separating from each other. Their purpose, as in other animals, is to guard the teeth, but they are more especially intended to serve a higher office, contributing in common with other parts to man’s faculty of speech. For just as nature has made man’s tongue unlike [660a1] that of other animals, and, in accordance with what I have said is her not uncommon practice, has used it for two distinct operations, namely for the perception of savours and for speech, so also has she acted with regard to the lips, and made them serve both for speech and for the protection of the teeth. For vocal speech consists of combinations of the letters, and most of these it would be [5] impossible to pronounce, were the lips not moist, nor the tongue such as it is. For some letters are formed by closures of the lips and others by applications of the tongue. But what are the differences presented by these and what the nature and extent of such differences, are questions to which answers must be sought from those who are versed in metrical science. It was necessary that the two parts which [10] we are discussing should from the start be severally adapted to fulfil the office mentioned above, and be of appropriate character. Therefore are they made of flesh, and flesh is softer in man than in any other animal, the reason for this being that of all animals man has the most delicate sense of touch.
[15] 17 · The tongue is placed under the vaulted roof of the mouth. In land animals it presents but little diversity. But in other animals it is variable, and this whether we compare them as a class with such as live on land, or compare their several species with each other. It is in man that the tongue attains its greatest degree of freedom, of softness, and of breadth; the object of this being to render it [20] suitable for its double function—both for the perception of savours (for man is the most sensitive of animals, and a soft tongue is most adapted to sensation, being most impressionable by touch, of which sense taste is but a variety), and its softness again, together with its breadth, adapts it for the articulation of letters and for [25] speech. For these qualities, combined with its freedom from attachment, are those which suit it best for advancing and retiring in every direction. That this is so is plain, if we consider the case of those who are tongue-tied in however slight a degree. For their speech is indistinct and lisping; that is to say there are certain letters which they cannot pronounce. In being broad is comprised the possibility of becoming narrow; for in the great the small is included, but not the great in the small.
What has been said explains why, even among birds, those that are most capable of pronouncing letters are such as have the broadest tongues; and why the [30] viviparous and sanguineous quadrupeds, where the tongue is hard and thick and not free in its motions, have a very limited vocal articulation. Some birds have a considerable variety of notes. These are the smaller kinds. But it is the birds with [35] talons that have the broader tongues. All birds use their tongues to communicate with each other. But some do this in a greater degree than the rest; so that in some [660b1] cases it even seems as though actual instruction were imparted from one to another. These, however, are matters which have already been discussed in the History of Animals.
As to those oviparous and sanguineous animals that live on land, their tongue in most cases is tied down and hard, and is therefore useless for vocal purposes; in [5] the serpents, however, and in the lizards it is long and forked, so as to be suited for the perception of savours. So long indeed is this part in serpents, that though small while in the mouth it can be protruded to a great distance. In these same animals it is forked and has a fine and hair-like extremity, because of their great liking for food. For by this arrangement they derive a twofold pleasure from savours, their gustatory sensation being as it were doubled. [10]
Even some bloodless animals have an organ that serves for the perception of savours; and in sanguineous animals such an organ is invariably present. For even in such of these as seem to most people to have nothing of the kind, some of the fishes for example, there is a kind of shabby representative of a tongue, much like what exists in river crocodiles. In most of these cases the apparent absence of the part can [15] be rationally explained on some ground or other. For in the first place the interior of the mouth in animals of this character is invariably spinous. Secondly, in water animals there is but short space of time for the perception of savours, and as the use of this sense is thus of short duration, shortened also is the separate part which [20] subserves it. The reason for their food being so rapidly transmitted to the stomach is that they cannot possibly spend any time in sucking out the juices; for were they to attempt to do so, the water would make its way in during the process. Unless therefore one pulls their mouth very widely open, the projection of this part is quite invisible. The region exposed by thus opening the mouth is spinous; for it is formed by the close apposition of the gills, which are of a spinous character. [25]
In crocodiles the immobility of the lower jaw also contributes in some measure to stunt the development of the tongue. For the crocodile’s tongue is adherent to the lower jaw. For its upper and lower jaws are, as it were, inverted, it being the upper jaw which in other animals is the immovable one. The tongue, however, of this animal is not attached to the upper jaw, because that would interfere with the [30] ingestion of food, but adheres to the lower jaw, because this is, as it were, the upper one which has changed its place. Moreover, it is the crocodile’s lot, though a land animal, to live the life of a fish, and this again necessarily involves an indistinct formation of the part in question.
[35] The roof of the mouth resembles flesh, even in many of the fishes; and in some of the river species, as for instance in the fishes known as Cyprini, is so very [661a1] flesh-like and soft as to be taken by careless observers for a tongue. The tongue of fishes, however, though it exists as a separate part, is never formed with such distinctness as this, as has been already explained. Again, the gustatory sensibility [5] is not diffused equally over the whole surface of the tongue-like organ, but is placed chiefly in the tip; and for this reason it is the tip which is the only part of the tongue separated in fishes from the rest of the mouth. As all animals are sensible to the pleasure derivable from food, they all feel a desire for it. For the object of desire is the pleasant. The part, however, by which food produces the sensation is not alike in [10] all of them, but while in some it is free from attachments, in others, where it is not required for vocal purposes, it is adherent. In some again it is hard, in others soft or flesh-like. Thus even the Crustacea, the crayfish for instance and the like, and the [15] Cephalopods, such as the cuttlefish and the octopus, have some such part inside the mouth. As for the Insects, some of them have the part which serves as tongue inside the mouth, as is the case with ants, and as is also the case with many Testacea, while in others it is placed externally. In this latter case it resembles a sting, and is hollow and spongy, so as to serve at one and the same time for the tasting and for the [20] sucking up of nutriment. This is plainly to be seen in flies and bees and all such animals, and likewise in some of the Testacea. In the purple murex, for instance, so strong is this part that it enables them to bore holes through the hard covering of shell-fish, of the spiral snails, for example, that are used as bait to catch them. So also the gad-flies and cattle-flies can pierce through the skin of man, and some of [25] them even through the skins of other animals. Such, then, in these animals is the nature of the tongue, which is thus as it were the counterpart of the elephant’s nostril. For as in the elephant the nostril is used as a defence, so in these animals the tongue serves as a sting.
[30] In all other animals the tongue agrees with the description already given.
1 · We have next to consider the teeth, and with these the mouth which they [661b1] enclose and form. The teeth have one invariable office, namely the reduction of food; but besides this general function they have other special ones, and these differ in different groups. Thus in some animals the teeth serve as weapons; but this with a distinction. For there are offensive weapons and there are defensive weapons; and [5] while in some animals, as the wild Carnivora, the teeth answer both purposes, in many others, both wild and domesticated, they serve only for defence. In man the teeth are admirably constructed for their general office, the front ones being sharp, so as to cut the food into bits, and the molars broad and flat, so as to grind it to a pulp; while between these and separating them are the canines which, in accordance [10] with the rule that the mean partakes of both extremes, share in the characters of those on either side, being broad in one part but sharp in another. Similar distinctions of shape are presented by the teeth of other animals, with the exception of those whose teeth are one and all of the sharp kind. In man, however, the number and the character even of these sharp teeth have been mainly determined by the requirements of speech. For the front teeth of man contribute in many ways to the [15] formation of letter-sounds.
In some animals, however, the teeth, as already said, serve merely for the reduction of food. When, besides this, they serve as offensive and defensive weapons, they may either be formed into tusks, as for instance is the case in swine, or may be sharp-pointed and interlock with those of the opposite jaw, in which case the animal is said to be saw-toothed. For the strength of such an animal is in its [20] teeth, and these depend for their efficiency on their sharpness. In order, then, to prevent their getting blunted by mutual friction, such of them as serve for weapons fit into each other’s interspaces. No animal that has saw-teeth is at the same time furnished with tusks. For nature never makes anything superfluous or in vain. She gives, therefore, tusks to such animals as strike in fighting, and serrated teeth to [25] such as bite. Sows, for instance, have no tusks, and accordingly sows bite.
A general principle must here be noted, which will be found applicable not only in this instance but in many others that will occur later on. Nature allots each weapon, offensive and defensive alike, to those animals alone that can use it; or, if [30] not to them alone, to them in a more marked degree; and she allots it in its most perfect state to those than can use it best; and this whether it be a sting, or a spur, or horns, or tusks, or what it may of a like kind.
Thus as males are stronger and more choleric than females, it is in males that such parts as those just mentioned are found, either exclusively, as in some species, or more fully developed, as in others. For though females are of course provided with such parts as are necessary to them, the parts, for instance, which subserve [35] nutrition, they have even these in an inferior degree, and the parts which answer no such necessary purpose they do not possess at all. This explains why stags have [662a1] horns, while does have none; why the horns of cows are different from those of bulls, and, similarly, the horns of ewes from those of rams. It explains also why the females are often without spurs in species where the males are provided with them, [5] and accounts for similar facts relating to all other such parts.
All fishes have teeth of the saw-toothed form, with the single exception of the fish known as the Scarus. In many of them there are teeth even on the tongue and on the roof of the mouth. The reason for this is that, living as they do in the water, they cannot but allow this fluid to pass into the mouth with the food. The fluid thus [10] admitted they must necessarily discharge again without delay. For they cannot spend time grinding their food, since the water would run into their digestive cavities. Their teeth therefore are all sharp, being adapted only for cutting, and are numerous and set in many parts, that their abundance may serve in lieu of any grinding faculty, to mince the food into small bits. They are also curved, because [15] they are almost the only weapons which fishes possess.
In all these offices of the teeth the mouth also takes its part; but besides these functions it is subservient to respiration, in all such animals as breathe and are cooled by external agency. For nature, as already said, uses the parts which are [20] common to all animals for many special purposes, and this of her own accord. Thus the mouth has one universal function in all animals alike, namely its alimentary office; but in some, besides this, the special duty of serving as a weapon is attached to it; in others that of ministering to speech; and again in many, though not in all, the office of respiration. All these functions are thrown by nature upon one single organ, the construction of which she varies so as to suit the variations of office. [25] Therefore it is that in some animals the mouth is contracted, while in others it is of wide dimensions. The contracted form belongs to such animals as use the mouth merely for nutritive, respiratory, and vocal purposes; whereas in such as use it as a means of defence it has a wide gape. This is its invariable form in such animals as are saw-toothed. For seeing that their mode of warfare consists in biting, it is advantageous to them that their mouth shall have a wide opening; for the wider it [30] opens, the greater will be the extent of the bite, and the more numerous will be the teeth called into play.
Biting and carnivorous fish have a mouth of that sort, whereas in the rest it is a tapering snout. For this form is suited for their purposes, while the other would be useless.
In birds the mouth consists of what is called the beak, which in them is a substitute for lips and teeth. This beak presents variations in harmony with the [662b1] functions and protective purposes which it serves. Thus in those birds that are called Crooked-clawed it is invariably hooked, inasmuch as these birds are carnivorous, and eat no kind of vegetable food. For this form renders it serviceable to them in obtaining the mastery over their prey, and is better suited for deeds of violence than [5] any other. Moreover, as their weapons of offence consist of this beak and of their claws, these latter also are more crooked in them than in the generality of birds. Similarly in each other kind of bird the beak is suited to the mode of life. Thus, in woodpeckers it is hard and strong, as also in crows and birds of crow-like habit, while in the smaller birds it is delicate, so as to be of use in collecting seeds and [10] picking up minute animals. In such birds, again, as eat herbage, and such as live about marshes—those, for example, that swim and have webbed feet—the bill is broad, or adapted in some other way to the mode of life. For a broad bill enables a bird to dig into the ground with ease, just as, among quadrupeds, does the broad snout of the pig, an animal which, like the birds in question, lives on roots. [15] Moreover, in these root-eating birds and in some others of like habits of life, the tips of the bill end in hard points, which gives them additional facility in dealing with herbaceous food.
The several parts which are set on the head have now, pretty nearly all, been considered. In man, however, the part which lies between the head and the neck is called the face, this name being, it would seem, derived from the function of the [20] part. For as man is the only animal that stands erect, he is also the only one that looks directly in front; and the only one whose voice is emitted in that direction.10
2 · We have now to treat of horns; for these also, when present, are appendages of the head. They exist in none but viviparous animals; though in some ovipara certain parts are metaphorically spoken of as horns, in virtue of a certain [25] resemblance. To none of such parts, however, does the proper office of a horn belong; for the vivipara have their horns for the sake of defence and attack, but this is not the case with any of the other creatures said to have horns; for they do not use their horns in defence or for mastery, which are tasks requiring strength. So also no [30] polydactylous animal is furnished with horns. For horns are defensive weapons, and these polydactylous animals possess other means of security. For to some of them nature has given claws, to others teeth suited for combat, and to the rest some other adequate defensive appliance. There are horns, however, in most of the cloven-hoofed animals, and in some of those that have a solid hoof, serving them as an [663a1] offensive weapon. Horns also serve for defence in all animals that have not been provided by nature with some other means of security; such means, for instance, as speed, which has been given to horses; or great size, as in camels; for excessive bulk, [5] such as has been given to these animals, and in a still greater measure to elephants, is sufficient in itself to protect an animal from being destroyed by others. Other animals again are protected by the possession of tusks; and among these are the swine, though they have a cloven hoof.
All animals again, whose horns are but useless appendages, have been provided by nature with some additional means of security. Thus deer are endowed with [10] speed; for the large size and great branching of their horns makes these a source of detriment rather than of profit to their possessors. Similarly endowed are the antelope and gazelle; for though these animals will stand up against some enemies and defend themselves with their horns, yet they run away from such as are fierce and pugnacious. The bison again, whose horns curve inwards towards each other, is provided with a means of protection in the discharge of its excrement; and of this it [15] avails itself when frightened. There are some other animals that have a similar mode of defence. In no case, however, does nature ever give more than one adequate means of protection to one and the same animal.
Most of the animals that have horns are cloven-hoofed; but the Indian ass, as they call it, is also reported to be horned, though its hoof is solid.
Again as the body, so far as regards its organs of motion, consists of two [20] distinct parts, the right and the left, so also and for the same reasons the horns of animals are, in the great majority of cases, two in number. Still there are some that have but a single horn; the oryx, for instance, and the so-called Indian ass; in the former of which the hoof is cloven, while in the latter it is solid. In such animals the [25] horn is set in the centre of the head; for as the middle belongs equally to both extremes, this arrangement is the one that comes nearest to each side having its own horn.
Again, it would appear consistent with reason that the single horn should go with the solid rather than with the cloven hoof. For hoof, whether solid or cloven, is [30] of the same nature as horn; so that the two naturally undergo division simultaneously and in the same animals. Again, since the division of the cloven hoof depends on deficiency of material, it is but rationally consistent, that nature, when she gave an animal an excess of material for the hoofs, which thus became solid, should have taken away something from the upper parts and so made the animal to have but one horn.
[35] Rightly too did she act when she chose the head whereon to set the horns; and Æsop’s Momus is beside the mark, when he finds fault with the bull for not having [663b1] its horns upon its shoulders. For from this position, says he, they would have delivered their blow with the greatest force, whereas on the head they occupy the weakest part of the whole body. Momus was but dull-sighted in making this hostile [5] criticism. For had the horns been set on any other part than they are, the encumbrance of their weight would have been increased, not only without any compensating gain whatsoever, but with the disadvantage of impeding many bodily operations—and similarly if they had been set on the shoulders. For the point whence the blows could be delivered with the greatest force was not the only matter to be considered, but the point also whence they could be delivered with the widest range. But as the bull has no hands and cannot possibly have its horns on its feet or on its knees, where they would prevent flexion, there remains no other site for them [10] but the head; and this therefore they necessarily occupy. In this position, moreover, they are much less in the way of the movements of the body than they would be elsewhere.
Deer are the only animals in which the horns are solid throughout, and are also the only animals that cast them. This casting is for the advantage of the deer from the increased lightness which it produces, but, seeing how heavy the horns are, it is also a matter of necessity.
[15] In all other animals the horns are hollow for a certain distance, and the end alone is solid, this being the part of use in a blow. At the same time, to prevent even the hollow part which grows out of the skin from being weak, the solid part fitted into it comes up from the bones. For this arrangement is not only that which makes the horns of the greatest service in fighting, but that which causes them to be as [20] little of an impediment as possible in the other actions of life.
Such then are the reasons for which horns exist; and such the reasons why they are present in some animals, absent from others.
Let us now consider the character of the material nature whose necessary results have been employed by rational nature for a final cause.
In the first place, then, the larger the bulk of animals, the greater is the [25] proportion of corporeal and earthy matter which they contain. Thus no very small animal is known to have horns, the smallest horned animal that we are acquainted with being the gazelle. But in all our speculations concerning nature, what we have to consider is the general rule; for that is natural which applies either universally or for the most part. Now all the bone in animals’ bodies is earthy; and that is why we [30] can say, if we consider what holds for the most part, that there is most earthy matter in the largest animals. At any rate, in the larger animals there is an excess of it, and this excess is turned by nature to useful account, being converted into weapons of defence. Part of it necessarily flows to the upper portion of the body, and this is allotted in some cases to the formation of tusks and teeth, in others to the formation [35] of horns. Thus it is that no animal that has horns has also front teeth in both jaws, those in the upper jaw being deficient. For nature by subtracting from the teeth [664a1] adds to the horns; the nutriment which in most animals goes to the former being here spent on the augmentation of the latter. Does, it is true, have no horns and yet are equally deficient with the males as regards the teeth. The reason, however, for this is that they, as much as the males, are naturally horn-bearing animals; but they [5] have been stripped of their horns, because these would be useless—indeed they are useless to the males too, but the males’ strength makes them less harmful. In other animals, where this material is not secreted from the body in the shape of horns, it is used to increase the size of the teeth; in some cases of all the teeth, in others merely [10] of the tusks, which thus become so long as to resemble horns projecting from the jaws.
So much, then, of the parts which appertain to the head.
3 · Below the head lies the neck, in such animals as have one. This is the case with those only that have the parts to which a neck is subservient. These parts are [15] the larynx and what is called the oesophagus. Of these the larynx exists for the sake of respiration, being the instrument by which animals inhale and discharge the air. Therefore it is that, when there is no lung, there is also no neck. Of this condition the [20] fishes are an example. The oesophagus is the channel through which food is conveyed to the stomach; so that all animals that are without a neck are also without a distinct oesophagus. Such a part is in fact not required of necessity for nutritive purposes; for it has no action whatsoever on the food. Indeed there is nothing to prevent the stomach from being placed directly after the mouth. This, however, is [25] impossible in the case of the lung. For there must be some sort of tube common to the two divisions of the lung, by which—it being bipartite—the breath may be apportioned to their respective bronchi, and thence pass into the air-pipes; and such an arrangement will be the best for producing inspiration and expiration. The organ then concerned in respiration must of necessity be of some length; and this, again, [30] necessitates there being an oesophagus to unite mouth and stomach. This oesophagus is of a flesh-like character, and yet admits of extension like a sinew. This latter property is given to it, that it may stretch when food is introduced; while the flesh-like character is intended to make it soft and yielding, and to prevent it from [35] being rasped by particles as they pass downwards, and so suffering damage. On the other hand, the windpipe and the so-called larynx are constructed out of a cartilaginous substance. For they have to serve not only for respiration, but also for [664b1] vocal purposes; and an instrument that is to produce sounds must necessarily be not only smooth but firm. The windpipe lies in front of the oesophagus, although this position causes it to be some hindrance to the latter when admitting food. For if a [5] morsel of food, fluid or solid, slips into it by accident, choking and much distress and violent fits of coughing ensue. This must be a matter of astonishment to any of those who assert that it is by the windpipe that an animal imbibes fluid. For the consequences just mentioned occur invariably, whenever a particle of food slips in, [10] and are quite obvious. Indeed on many grounds it is ridiculous to say that this is the channel through which animals imbibe fluid. For there is no passage leading from the lung to the stomach, such as the oesophagus which we see leading thither from the mouth. Moreover, when any cause produces sickness and vomiting, it is plain enough whence the fluid is discharged. It is manifest also that fluid does not pass [15] directly into the bladder and collect there, but goes first into the stomach. For, when red wine is taken, the excreta from the stomach are seen to be coloured by its dregs; and such discoloration has been even seen on many occasions where there have been wounds opening into the stomach. However, it is perhaps silly to be minutely particular in dealing with silly statements such as this.
[20] The windpipe then, owing to its position in front of the oesophagus, is exposed, as we have said, to annoyance from the food. To obviate this, however, nature has contrived the epiglottis. This part is not found in all viviparous animals, but only in such of them as have a lung and a skin covered with hairs, and not either with scaly [25] plates or with feathers. In the latter animals, instead of an epiglottis the larynx closes and opens, just as in the other case the epiglottis falls down and rises up; rising up during the ingress or egress of breath, and falling down during the ingestion of food, so as to prevent any particle from slipping into the windpipe. [30] Should there be the slightest want of accuracy in this movement, or should an inspiration be made during the ingestion of food, choking and coughing ensue, as already has been noticed. So admirably contrived, however, is the movement both of the epiglottis and of the tongue, that, while the food is being ground in the mouth [35] and passing over the epiglottis, the tongue very rarely gets caught between the teeth and seldom does a particle slip into the windpipe.
[665a1] The animals which have been mentioned as having no epiglottis owe this deficiency to the dryness of their flesh and to the hardness of their skin. For an epiglottis made of such materials would not admit of easy motion. It would, indeed, take a longer time to shut down an epiglottis made of the peculiar flesh of these [5] animals, and shaped like that of those with hairy skins, than to bring the edges of the windpipe itself into contact with each other.
Thus much then as to the reason why some animals have an epiglottis while others have none. It is a contrivance of nature to remedy the unsatisfactory position [10] of the windpipe in front of the oesophagus. That position is the result of necessity. For it is in the front and centre of the body that the heart is situated, in which we say is the principle of life and the source of all motion and sensation. (For sensation and motion are exercised in the direction which we term forwards, and it is on this very [15] relation that the distinction of before and behind is founded.) But where the heart is, there and surrounding it is the lung. Now inspiration, which occurs because of the lung and the principle which has its seat in the heart, is effected through the windpipe. Since then the heart must of necessity lie in the very front place of all, it follows that the larynx also and the windpipe must of necessity lie in front of the [20] oesophagus. For they lead to the lung and heart, whereas the oesophagus leads to the stomach. And in general, as regards above and below, front and back, right and [25] left, the nobler and more honourable part invariably is placed uppermost, in front, and on the right, unless some more important object stands in the way.
4 · We have now dealt with the neck, the oesophagus, and the windpipe, and have next to treat of the viscera. These are peculiar to sanguineous animals, some of which have all of them, others only a part, while no bloodless animals have any at [30] all. Democritus then seems to have been mistaken in the notion he formed of the viscera, if, that is to say, he fancied that the reason why none were discoverable in bloodless animals was that these animals were too small to allow them to be seen. For, in sanguineous animals, both heart and liver are visible enough when the body is only just formed, and while it is still extremely small. For these parts are to be seen in the egg sometimes as early as the third day, being then no bigger than a point; and are visible also in aborted embryos, while still excessively minute. [665b1] Moreover, as the external organs are not precisely alike in all animals, but each creature is provided with such as are suited to its special mode of life and motion, so is it with the internal parts, these also differing in different animals. Viscera, then, [5] are peculiar to sanguineous animals; and therefore are all formed from sanguineous material, as is plainly to be seen in the new-born young of these animals. For in such the viscera are more sanguineous, and of greater bulk in proportion to the body, it being in the earliest stage of formation that the nature of the material and its abundance are most conspicuous. There is a heart, then, in all sanguineous animals, [10] and the reason for this has already been given. For that sanguineous animals must necessarily have blood is self-evident. And, as the blood is fluid, it is also a matter of necessity that there shall be a receptacle for it; and it is apparently to meet this requirement that nature has devised the blood-vessels. These, again, must necessarily have one primary source. For it is preferable that there shall be one such, [15] when possible, rather than several. This primary source of the vessels is the heart. For the vessels manifestly issue from it and do not go through it. Moreover, being as it is homogeneous, it has the character of a blood-vessel. Again its position is that of a primary part. For nature, when no other more important purpose stands in her way, places the more honourable part in the more honourable position; and the [20] heart lies about the centre of the body, but rather in its upper than its lower half, and also more in front than behind. This is most evident in the case of man, but even in other animals there is a tendency in the heart to assume a similar position, in the centre of the necessary part of the body, that is to say of the part which terminates in the vent for excrement. For the limbs vary in position in different animals, and [25] are not to be counted with the parts which are necessary for life. That is why life can be maintained even when they are removed; while it is self-evident that the addition of them to an animal is not destructive of it.
There are some who say that the vessels commence in the head. In this they are mistaken. For in the first place, according to their representation, there would be many sources for the vessels, and these scattered; and secondly, these sources would [30] be in a region that is manifestly cold, as is shown by its intolerance of chill, whereas the region of the heart is hot. Again, as already said, the vessels continue their course through the other viscera, but no vessel passes through the heart. From this it is quite evident that the heart is a part of the vessels and their origin; and for this it is well suited by its structure. For its central part consists of a dense and hollow [666a1] substance, and is moreover full of blood, as though the vessels took thence their origin. It is hollow to serve for the reception of the blood, while its wall is dense, that it may serve to protect the source of heat. For here, and here alone in all the viscera [5] and indeed in all the body, there is blood without blood-vessels, the blood elsewhere being always contained within vessels. Nor is this but consistent with reason. For the blood is conveyed into the vessels from the heart, but none passes into the heart from without. For this constitutes the origin and fountain, or primary receptacle, of [10] the blood. It is, however, from dissections and from observations on the process of development that the truth of these statements receives its clearest demonstration. For the heart is the first of all the parts to be formed; and no sooner is it formed than it contains blood. Moreover, the motions of pain and pleasure, and generally of all sensation, plainly have their source in the heart, and find in it their termination. This, indeed, reason would lead us to expect. For the source must, whenever [15] possible, be one; and, of all places, the best suited for a source is the centre. For the centre is one, and is equally or almost equally within reach of every part. Again, as neither the blood itself, nor yet any part which is bloodless, is endowed with sensation, it is plain that that part which first has blood, and which holds it as it were in a receptacle, must be the primary source. And that this part is the heart is [20] not only a rational inference, but is also evident to the senses. For no sooner is the embryo formed, than its heart is seen in motion as though it were a living creature, and this before any of the other parts, it being, as thus shown, the starting-point of their nature in all animals that have blood. A further evidence of the truth of what has been stated is the fact that no sanguineous animal is without a heart. For the primary source of blood must of necessity be present in them all. It is true that [25] sanguineous animals also invariably have a liver. But no one could ever deem the liver to be the primary organ either of the whole body or of the blood. For the position in which it is placed is far from being that of a primary part; and, moreover, in the most perfectly finished animals there is another part, the spleen, which as it were counterbalances it. Still further, the liver contains no receptacle for blood, as [30] does the heart; but its blood is in a vessel as in all the other viscera. A vessel, moreover, extends through it, and no vessel extends through the heart; for it is from the heart that all the vessels take their rise. Since then one or other of these two parts must be the central source, and since it is not the liver which is such, it follows of necessity that it is the heart which is the source of the blood. For the definitive [35] characteristic of an animal is the possession of sensation; and the first sensory part is that which first has blood; that is to say is the heart, which is the source of blood [666b1] and the first of the parts to contain it.